Insulated Glass Units with Variable Light Transmission Structures

ABSTRACT

This disclosure includes variable light transmission panels (VLTPs) and their assembly into insulated glass units (IGUs), which can be incorporated into buildings. Disclosed windows provide uniform appearance from outside during the day when a number of such windows are incorporated in a building regardless of their state of light transmission. These disclosures may also be used to make windows which tint to different transmitted colors but during the day still appear to be uniform from outside.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.17/226,238, filed on Apr. 9, 2021, which claims priority benefit of U.S.provisional application 63/007,389 filed on Apr. 9, 2020, the entirecontents of which are incorporated herein by reference.

FIELD OF THE INVENTION

This disclosure relates to variable transmission windows which are usedfor architectural and transportation applications. VLTPs may befabricated using electrochromic and other technologies. In thisdisclosure, the appearance of such windows is addressed when thebuildings and vehicles are viewed from outside.

BACKGROUND

The light transmission properties of variable light transmission panels(VLTPs) change by application of an electrical stimulus. In thisinvention, the principles of novelty will be explained usingelectrochromic (EC) technology although these principals will also bevalid for other types of VLTPs such as those using liquid crystallinematerials and suspended particles. When electrically controlled VLTPdevices are fabricated using transparent substrates, these devices uponapplication of an electric voltage change their optical state, i.e.,color, opacity, and/or transparency (light transmission or reflection).A user (or a user defined control system) can select and switch from onetransmission state to the other. VLTP devices are referred to as “smartglass” or “smart windows” as the optical characteristics of the windowswith these elements adapt to the weather or user defined conditions.Used in buildings, these smart windows may provide shade, glarereduction, energy savings, privacy, partitions and so forth. There is agreat interest in the use of EC devices containing VLTPs for at leastone of the above reasons in building windows, and in windows fortransportation including cars, buses, trains, boats/ships and airplanes.

Used in construction of windows for residential and commercial buildingsand in transportation, these windows with EC VLTPs result in energyefficient building envelopes and increased comfort by regulating thesolar energy penetration through the windows. These windows includewindows located within the door including transoms and sidelights. Thesewindows may be fixed or movable, where the latter includes double-hungand casement windows and sliding windows and sliding glass doors.Building glass exteriors are designed by considering several parameterswhich include aesthetics, environment, location, etc., while alsoproviding proper indoor daylighting, glare control so as to consume lessenergy for lighting, heating, ventilation and air-conditioning (HVAC).While use and characteristics of VLTP have been extensivelyinvestigated, but much attention has not been paid to its externalappearance. For windows with VLTP panels such as EC technology where auser (or a person inside the building) makes a selection of the lighttransmission properties of these windows, this action inadvertentlychanges the exterior appearance of the window, i.e., windows indifferent optical states lead to differences in appearance which resultsin a checkerboard effect when such a building is viewed during the day.In most situations this is undesirable.

SUMMARY OF THE INVENTION

In a first aspect, the present disclosure includes an electrochromicvariable light transmission panel (VLTP). In some aspects, a VLTP of thepresent disclosure may include (a) two transmissive substrates arrangedin a parallel configuration; (b) the first substrate having two sideswherein the second side is coated with a coating stack comprising of atleast two layers, followed by a coating of a transparent conductor andfurther followed by an EC layer; and (c) an electrolyte layer disposedbetween the two substrates, wherein the electrolyte layer contacts thesaid EC layer. In some aspects, a VLTP of the present disclosure mayshow a color difference ΔE_(T)* of greater than 40 in transmitted colorwhen measured in the bleached and the colored optical states, and inthese optical states show a color difference ΔE_(R)* of less than 6 whenreflection is viewed from a side of the VLTP. In some aspects, the sideof the VLTP is a side that faces the outside of a building.

In one aspect, the present disclosure includes an insulated glass unit(IGU) assembly comprising the VLTP of the present disclosure. In someaspects, the IGU assembly contains at least one low-e coated panel inaddition to the VLTP; and the IGU show a color difference ΔE_(T)* ofgreater than 40 in transmitted color when compared in the bleached andthe colored optical states of the VLTP, and these optical states show acolor difference ΔE_(R)* of less than 8 when reflection is viewed fromthe first side of the VLTP.

In one aspect, the present disclosure includes a window including theVLTP, which further has a film bonded to the second substrate on theside that is not facing the electrochromic medium, and the said filmhaving a low-e surface.

In one aspect, the present disclosure includes an electrochromicvariable light transmission panel (VLTP) comprising a first transmissivesubstrate and a second transmissive substrate arranged in a parallelconfiguration, wherein the first transmissive substrate has a first sideand a second side, wherein the second side is coated with a stack ofcoatings comprising at least two layers, followed by a coating of atransparent conductor, wherein the second transmissive substrate has afirst side and a second side, wherein the first side of the secondtransmissive substrate is coated with a transparent conductor, whereinthe substrates are disposed in an assembly such that an electrochromicmedium is disposed between the conductive sides of the two substrates.In one aspect, the VLTP shows a color difference ΔE_(T)* of greater than40 in transmitted color when measured in the bleached and the coloredoptical states, and shows a color difference of ΔE_(R)* of less than 6when reflection is viewed from the first side of the first substrate.

In one aspect, the present disclosure includes an insulated glass unit(IGU) assembly having a VLTP, wherein the said IGU assembly comprises atleast one low-e coated panel in addition to the said VLTP; and the saidIGU assembly shows a color difference ΔE_(T)* of greater than 40 intransmitted color when compared in the bleached state and the coloredoptical states of the VLTP, and in these optical states of the VLTP, theIGU assembly shows a color difference in reflected color ΔE_(R)* of lessthan 8 when reflection is viewed from the first side of the VLTP.

In one aspect, the present disclosure includes an electrochromicvariable light transmission panel (VLTP) comprising a first transmissivesubstrate and a second transmissive substrate arranged in a parallelconfiguration; wherein the first substrate comprises a first side and asecond side, wherein the second side is coated with a stack of coatingscomprising at least two layers, followed by a coating of a transparentconductor; wherein the second substrate comprises a first side and asecond side, wherein the first side of the second substrate is coatedwith a transparent conductor; wherein the substrates are configured inan assembly such that an electrochromic medium is disposed betweenconductive sides of the first and second substrates; wherein the saidVLTP shows a transmission ratio of greater than 2.5 at 550 nm whenmeasured in the bleached and the colored states, and, in these opticalstates, shows ΔE_(R)* of less than 6 when reflection is viewed from thefirst side of the first substrate.

In one aspect, the present disclosure includes an insulated glass unit(IGU) assembly comprising at least one low-e coated panel and a VLTPseparated by a gap, wherein the VLTP comprises: a first transmissivesubstrate and a second transmissive substrate arranged in a parallelconfiguration; wherein the first substrate comprises a first side and asecond side, wherein the second side is coated with a coating stackcomprising at least two layers, followed by a coating of a transparentconductor and further followed by a EC layer; and an electrolyte layerdisposed between the first and second substrates, wherein theelectrolyte layer contacts the said EC layer; wherein the said IGUassembly shows a color difference ΔE_(T)* of greater than 40 intransmitted color when compared in the bleached and the colored opticalstates of the VLTP, and in these optical states, shows a colordifference ΔE_(R)* of less than 8 when reflection is viewed from thefirst side of the first substrate.

In one aspect, the present disclosure includes an insulated glass unit(IGU) assembly comprising at least one low-e coated panel and a VLTPseparated by a gap, wherein the VLTP comprises: a first transmissivesubstrate and a second transmissive substrate arranged in a parallelconfiguration; wherein the first transmissive substrate comprises afirst side and a second side, wherein the second side is coated with astack of coatings comprising at least two layers, followed by a coatingof a transparent conductor; wherein the second transmissive substratecomprises a first side and a second side, wherein the first side iscoated with a transparent conductor; wherein the first and secondsubstrates are configured in an assembly such that an electrochromicmedium is disposed between conductive sides of the first and secondsubstrates; and the said IGU assembly shows a color difference ΔE_(T)*of greater than 40 in transmitted color when compared in the bleachedand the colored optical states of the VLTP, and, in these opticalstates, shows a color difference ΔE_(R)* of less than 8 when reflectionis viewed from the first side of the first substrate.

Other features and characteristics of the subject matter of thisdisclosure, as well as the methods of operation, functions of relatedelements of structure and the combination of parts, and economies ofmanufacture, will become more apparent upon consideration of thefollowing description and the appended claims, all of which form a partof this specification.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a schematic representation of a building with windowscontaining VLTP panels made using prior art and of a building with VLTPpanels as taught in the current invention;

FIGS. 2a and 2b illustrate schematics of a generic (prior art) EC (VLTP)devices;

FIG. 3 illustrates a schematic of an insulated glass unit (IGU)containing an EC VLTP of FIG. 2 a;

FIG. 4 illustrates schematics of several types of EC (VLTP) devices madeusing the teachings of the present disclosure;

FIG. 5 illustrates a schematic of an insulated glass unit (IGU)containing an EC VLTP of FIG. 4;

FIG. 6 illustrates a schematic of an insulated glass unit (IGU)containing an EC VLTP of FIG. 2b which is modified according to thepresent disclosure;

FIGS. 7a-7e show schematics of the front glass substrates and thetransparent conductive coatings for use in EC devices using theteachings of the present disclosure;

FIG. 8 illustrates a schematic view of the angular relationship betweena viewer and the glass façade of a building.

FIG. 9: Change in ΔE_(T)* and % transmission at 550 nm for EC panelswith and without interference stacks, as these panels color and bleachover a period of time.

FIG. 10: Change in ΔE_(T)* and ΔE_(R)* for EC panels with and withoutinterference stacks, as these panels color and bleach over a period oftime.

FIG. 11: correlation between the change in ΔE_(R)* versus ΔE_(T)* andTransmission ratio (at 550 nm) vs ΔE_(T)* for EC panels with and withoutinterference stacks, as these transition from a bleached state to acolored state.

DETAILED DESCRIPTION

While aspects of the subject matter of the present disclosure may beembodied in a variety of forms, the following description is merelyintended to disclose some of these forms as specific examples of thesubject matter encompassed by the present disclosure. Accordingly, thesubject matter of this disclosure is not intended to be limited to theforms or embodiments so described.

A first objective of this disclosure includes obtaining certain opticalproperties which result in desirable appearance of a building glassexterior when these EC devices (or VLTPs) are incorporated in thewindows. These optical properties allow the external glass façade ofthese buildings to visually appear largely unchanged during the day evenif the optical state of VLTP changes. The VLTPs are typically used inthe buildings in an IGU configuration. Stated differently, according tothe principles of this disclosure, when the various VLTPs in a buildingfaçade are in different optical states of light transmission, it isdifficult to notice visual differences between them from the outside ofthe building for a casual viewer during the daytime. FIG. 1 shows athree storied building with windows having VLTP panels on the second andthe third floors. Building A uses VLTP windows made using prior art,where a viewer standing outside of the building during the day noticesthat the windows 3 and 6 have a different optical appearance. This iscaused by the users inside the building who decide to darken thesewindows, i.e., reduce light or optical transmission which is best suitedto the activity that they are pursuing in the space dominated by thatwindow. This then results in a checkered appearance as seen by anobserver who is standing outside the building and is able to observe anumber of windows at the same time. This is not a pleasing aesthetic andan architect or a building owner may want to avoid such an appearance.It is desirable for the occupants of the rooms with windows 3 and 6 toexperience different light transmission, but from outside the glass ofthe windows should appear uniform during the day. A building which haswindows made from the present invention appears uniform as seen forBuilding B in FIG. 1, even though the states of transmission for VLTPwindows 3 and 6 are different from others, a casual observer outside maynot be able to discern the difference.

Design aspects of the VLTPs, including characteristics of substratesused to fabricate the VLTPs result in certain optical properties thatminimize the differences between the windows when seen from outsideduring the day, even if these panels are used in an IGU configurationwhere these panels are combined with an additional transmissive panelhaving a low-e coating by leaving a space filled with air or a lowthermal conductivity gas.

Achieving the above features in windows with VLTP opens up many morenovel aspects which have not been achieved in windows comprising VLTPsystems installed in buildings. In one novel aspect, this allows anarchitect to match windows with VLTPs with those windows which do nothave a VLTP element (e.g., a normal IGU window) and spandrels. Thismeans that during the daytime an outside casual viewer will havedifficulty in distinguishing which of these windows are those that havea VLTP element, and furthermore which of these VLTPs are in differentoptical states. This allows an architect to design a building which hasa unified appearance from outside but uses certain windows which haveVLTP elements and other windows or spandrel that do not have theseelements (static windows and static spandrels). This may be desirablefor many reasons, where the higher cost VLTP elements are only installedin select windows such as atriums and other common places or for certainoccupants who prefer VLTP comprising windows; and windows with VLTP maynot be installed on the north side of the building (in the northernhemisphere) where there is no direct solar glare; all of this can bedone without detracting from the aesthetic appearance of the building.Windows with VLTP elements may even be replaced temporarily orpermanently by static transmission windows or windows with VLTP ofdifferent transmitted color without causing a detraction in its externalappearance. This may also be desirable for engineering, procurement, andconstruction contractors to enable more cost-efficient buildings.

A second related objective of the present disclosures includes windowswith VLTP elements that provide building architects with externalreflected and internal transmitted color combinations and options whichwere previously not feasible. For example, the windows with VLTPelements could appear a desired shade of bronze, blue, green, gray onthe outside and appear similar or a vastly different color and hue fromthe inside (transmitted color). More specifically and functionally,these windows may darken to different internal transmitted colors (e.g.,green, blue, brown and neutral, or any combination of colors, etc.), butwith similar appearance from outside. This allows a building architectto select from various combinations of internal transmitted and externalreflected colors, i.e., independently customizing the individualinternal appearance (light transmission) and external appearance. Thisinnovation provides architects a freedom to design windows for differentbuildings, and also provides architects with a wider freedom to designwindows within the same building that may be customized for differentoccupants while keeping the same external appearance.

Electrochromic VLTPs which can be most effectively made by thisdisclosure contain two coated substrates separated by an electrolytelayer of above 10 and up to 2,000 microns in thickness. The frontsubstrate refers to the substrate that faces the outside of the windowsystem, i.e., it has an outdoor exposure. The uniform outdoor appearanceis achieved by one or more of the following: (a) increasing thereflectivity from the first substrate which is achieved by introductionof a reflective coating, particularly including reflective coatingstacks using interference which are placed on the substrate before theoutside light enters EC medium; and (b) optionally combining reflectivestacks with a tint in at least one of the coatings in this stack and/orthe substrate itself, which would also impact the color of the reflectedlight. Any specific coating or electrolyte within the VLTP panel whichchanges its optical properties due to the application of voltage iscalled as variable light transmission medium (VLTM).

For the VLTP windows the use of interference stacks would bedemonstrated in this disclosure to reflect part of the daylight toproject uniform appearance. The transmitted color in the device isdominated by the remainder of the light entering the device so that itcan be modulated by the color or the optical density of the EC mediumthat changes its color properties as it darkens upon the application ofvoltage.

The reflectivity of the interference stack on the front substrate isdependent on the thickness of the layers comprising this stack and alsothe refractive indices of the materials used to make these layers. Inthe EC devices of this disclosure, the interference stack is placedbetween the front substrate followed by the transparent conductorcoating (TC). Since the interference coating stacks work by thereflection and phase changes of light passing through the various layersof different thicknesses and refractive indices, the TC coating, due toits thickness and RI properties, also influences the reflectionperformance of this stack. Thus, any optimization of the reflectivityfrom this stack must take into account the transparent conductor (TC),i.e., its refractive index and thickness. In addition, the conductivityof the TC for window devices is high as they are typically largedevices, greater than 500 sq cm, and more generally greater than 800 sqcm Minimum surface resistivity for these windows is about 20Ω/□ (ohmsper square), and generally in the range of about 2 to 20Ω/□. Since theresistivity decreases with increasing TC thickness, appropriatethickness of the TC that will give the required resistivity must befactored in.

In some types of EC devices, a thin EC coating is placed on top of theTC. Generally, if this coating is in the range of less than 1,000 nm(for example 50 nm to 1000 nm, and any range therein is encompassed bythis disclosure) this will also influence the performance of theinterference stack. In that case its thickness and refractive index (RI)both in the bleached and the colored state will be important. However,its thickness should be sufficient to provide reasonable electrochromicactivity and should be optimized. In case such coatings of EC materialsare used on the front substrate, those EC materials are preferred wherethe change in real part of the refractive index in the fully colored tofully bleached state within the visible wavelengths is less than 20%,and in another embodiment less than 10% so that its influence is smallon the performance of the reflectivity of the reflective stack.

Interference coating stacks comprise at least two layers of dissimilarrefractive index. These are used in many types of optical devicesincluding optical communications and displays to optimize certainwavelength transmissions. For example, in rear-view EC mirrors for carsinterference stacks are used for optimization of the display quality.Since these are primarily reflective devices and displays are mounted onthe back of the mirrors, the optical emission from these displays ismaximized (or increased) through the reflective layers for specificwavelengths by use of interference stacks. These interference stacksalways contain a metallic reflectance layer, where the reflectivity ofthe metal layer is high. For example, these mirrors will have areflectivity in the range of about 40 to 80% in clear state, whichdecreases to about 4-8% in the dark state. It is important that thesemirrors have high reflectivity from the metallic layers so that clearimages are seen in rear-view mirrors, and the display light can also beprojected through these reflectors without giving double or ghostimages. Examples of these rear-view mirrors can be found in U.S. Pat.Nos. 8,400,704 and 7,009,751.

Further, as discussed below, in one preferred embodiment, the EC devicecomprises an electrolytic EC medium that is in contact with the two TCson the two opposing substrates. Examples of EC mediums that may be usedin these devices may be found in U.S. Pat. No. 5,611,966. In anotherpreferred embodiment a first EC coating in a thickness of less thanabout 1,000 nm is deposited following the TC on the front substrate, andan electrolyte which is in contact with the first EC coating. Examplesof such electrolytes and EC coatings are found in U.S. Pat. Nos.6,266,177 and 7,372,610. Furthermore, U.S. Pat. No. 10,760,334 disclosesEC layer compositions in EC devices containing electrochromic materialand conductive particles. Outdoor solar lighting (daylight) can varysubstantially during the day and under bright conditions may vary fromabout 120,000 lux to about 10,000 lux, where the former number isachieved under direct sun, and the latter number where the sun is notdirect. The other factors which influence the daytime solar intensityare cloud cover, time of the day, time of the year, thus the outsidelight intensity in the daytime in many instances can be lower than10,000 lux, down to 2000 lux. Examples of indirect sun are north side ofa building in Northern hemisphere (opposite in the southern hemisphere),under a shade or under cloudy but still bright sky conditions. Mostoffice and task lightings range from about 100 to 500 lux. Thus,daylight entering into a window even with a 50% visible lighttransmission may be reflected from the bright colored objects inside thebuilding and still would have a higher luminosity as compared to anyadded luminosity from the interior lighting. Thus if a substantialamount of light is reflected from a window with a VLTP element, prior tocontacting the variable light transmission element present in the saidVLTP, such windows will appear unchanged in appearance to an outsideobserver regardless of the optical state of the VLTP. A person in theinterior of the building desires to see a large change in lighttransmission (appearance) so as to shade the interior as intended.

Color (or appearance) of an object can be established by measuringreflected and/or transmitted light using color coordinates. There areseveral coordinate systems used to measure color which aremathematically related. A commonly used three-coordinate system called“L* a* b*” will be used to teach the novelty of this innovation. Thecolor difference in reflection or in transmission ΔE* between twoobjects or between two windows (or between two different optical statesof a VLTP) using this color system of coordinates is computed as givenbelow.

ΔE*=Sgrt{(L ₂ *−L ₁*)²+(a ₂ *−a ₁*)²+(b ₂ *−b ₁*)²}

Similarly, when an object darkens, the color shift (or change in hue)ΔE*_(H) is represented by

ΔE* _(H)=Sqrt{(a ₂ *−a ₁*)²±(b ₂ *−b ₁*)²}

Unless mentioned otherwise the colors when measured at narrow anglesusing D65 illuminant in the visible range use an observer which subtendsan angular vision of two or ten degrees (e.g., see the standard testmethod ISO/CIE 11664-4:2019 [CIE LEAD], Colorimetry—Part 4: CIE 1976L*a*b* color space; International Organization for Standardization,Geneva, Switzerland). ΔE_(R)* refers to the color difference inreflection and ΔE_(T)* refers to color change in transmission, and thecolor-shift or change in hue in reflection is given by ΔE_(R-H)* and thesame in transmission by ΔE_(T-H)*.

In the above equation L₁*a₁*b₁* and L₂*a₂*b₂* are the color coordinatesof the light being observed from two objects or from the same object indifferent optical states. L* value ranges from 0 to 100, wheredecreasing L* value represents a darker object, which at value zero isblack and devoid of any color. At L*=100 the color is white and iswashed out of all colors. All L*, a* and b* values form a sphere, wherethe colors are most vivid when L*=50. At that point the maximum andminimum values of a* are +60 (red) to −60 (green) and b* also rangesfrom 60 (yellow) to −60 (blue). The maximum absolute values of a* and b*decrease as L value changes from 50 in either direction.

When two windows or two similar VLTPs, but in different optical statesare observed in reflected light, the difference in color is given byΔE_(R)* and the color shift is given by ΔE_(R-H)*; when looking attransmitted light at these we can express these as ΔE_(T)* and ΔE_(T-H)*respectively. Where the subscripts R, T and H stand for reflection,transmission, and color-shift (hue) respectively. For example, a casualobserver located outside during daytime is able to easily discerndifference in two objects when ΔE_(R)* from reflected colors is below acertain threshold value. Typically, a near color match where ΔE_(R)* ofabout below 3 is good for certain embodiments, in some other embodimentsa color match may be considered acceptable when ΔE_(R)* is equal orbelow 6, and in some others a value of about 8 may also be acceptablewhere the hue differences are small, e.g., ΔE_(R-H) being less than 4.The above are the general teachings for ΔE_(R)*, but in some cases thethreshold of ΔE_(R)* may depend on where the locations of the two bodiesare in the color sphere (i.e., the absolute values of L*, a*, b*) due tovarying eye sensitivity. Thus, as described earlier that buildingwindows having VLTP elements may be in different optical states or maycolor to different transmitted colors. Therefore, in various embodimentsas will be discussed in this disclosure, the color match range inreflection (or ΔE_(R)* range) is below 8, in another embodiment below 6,yet in another embodiment below 3. For practical considerations perfectmatch is difficult to achieve thus a match within 0.3 or above isacceptable, and in other embodiments a match above 1 is also good.Please note that these ΔE_(R)* and ΔE_(R-H)* considerations apply toVLTP panels when used as windows, the panels themselves or when thesepanels are integrated in an IGU. Integration of these VLTP panels in IGUin most cases increase ΔE_(R)*, thus the choice of Low-e glass to makethis IGU is important.

In prior art windows with VLTP the change in transmission from thebleached state to the colored state will also cause a change in exteriorappearance with a ΔE_(R)* greater than the values stated above. In casethe VLTP optical transmission is only changed a little, then one willnot see a big difference in reflected colors, therefore one must definea minimum change in the transmitted light (or the degree of darkening)under which the reflected colors are measured and matched. Thus, for theabove color matches to be meaningful in the reflected color, thereshould be a large change in the transmitted color. When the variablelight transmission panels are colored to different depths which ininitial stages would impact its reflectivity, it is important toestablish minimum values of ΔE_(T)* for which the change in reflectivecolor ΔE_(R)* is to be established. For samples where the minimumΔE_(T)* is exceeded, and ΔE_(R)* is still within the desired range thatsample would also be deemed to have met the criteria of reflective colorchange at the minimum value of ΔE_(T)*. The large change in transmittedcolor can also be defined as ΔE_(T)* above 40 in one embodiment, above50 in another embodiment and above 60 in yet another embodiment. Anotherway to express the transmitted color could be the ratio of transmittedlight in the bleached to the colored state at 550 nm (which is close tothe photopic peak, also called transmission ratio). The EC panels shouldshow at least 2.5:1 in one embodiment and at least 5:1 in anotherembodiment or any range in between or at or beyond 10:1.

Published US patent application 20140085701 and U.S. Pat. No. 9,091,896have attempted to address an issue with windows with EC VLTP elements sothat the difference in reflected coloration as seen from the outside ofthe building are low. In particular, the attempt is to minimize thedifference in color perception between a small angle observation and alarge angle observation. This means that when an observer is standingclose to a tall building the angle of the observer's vision of thewindows at his height will be close to zero degrees (measured normal tothe surface of the window) and when the observer looks at the upperstories, the angle subtended is large (see FIG. 8). These publicationsteach that by attaching (or laminating) an additional glass element withreflective coating to a VLTP element could minimize the color differencebetween these stories. However, even in this publication, the goal ofachieving distinct transmitted colors or coloration density withoutimpacting the outside reflected color was not achieved as taught bycurrent embodiments, where this is being done by adding additionalcoatings and tuning the color of the front panel used to fabricate theVLTP.

In the present disclosure, even though different stories may appear tohave a different color, the important advantage of this innovation is tohave very little discernable difference between the windows which arecolored and not colored when they subtend the same angle. In oneembodiment the difference in reflectivity and color of the reflectedlight between different optical states should not be discernable by anobserver during the day at small angles (typically 0 to 12 degreesbetween the observer and the glass (angle being measured normal to theglass, see FIG. 8). In another embodiment the difference in reflectivityand color of the reflected light between different optical states shouldnot be discernable by an observer during the day at large angles(typically 30 to 45 degrees between the observer and the glass (anglebeing measured normal to the glass, see FIG. 8. FIG. 8 shows a side viewof a building façade with windows as 51 which is being seen by anobserver outside the building with the eye of the observer as 52. Whenthe observer looks at the windows which are close to his eye level, thenthe angle is small as shown by S. The normal to the glass is shown asNS. When the observer looks at a window far on the left side or theright side or towards an upper story then the angle subtended is wideras indicated by W and the normal to the glass is shown as NW. Sincethese angles are different and a significant reflection comes from thecoating stack, these colors may be different, but to an outside observerwindows in different optical states and next to each other making aboutthe same angle should look similar in appearance. The inclusion of anappropriate interference layer as taught in the current disclosure, andthe optional tint of the front substrate or one or more layers of theinterference stack, all prior to the light entering the EC medium, canalso result in small but acceptable change in color between the low andthe wide angles, while still providing little visual difference betweenVLTP windows from the outside regardless of their optical state.

In buildings where glass with EC VLTPs is installed, it is still easy todiscern the difference during daytime between the windows with coloredEC elements and those which are not colored. The above publication doesnot address the issue of uniform window appearance that are closetogether and at about the same angle of observation or even at differentangles of observation. Although the color teachings of the presentdisclosure may be also achieved by laminating an extra sheet of glasswith the optical properties taught herein on a VLTP containing windowsystem so that the optical state of the VLTP may be masked at smallangle or at a large angle, however that is not a preferred method due toincrease in weight, increase in total thickness reasons and additionalmanufacturing steps required for incorporating additional glass.

FIGS. 2a and 2b show a typical EC element which are used for fabricatingVLTPs. FIG. 2a shows a pair of clear transparent substrates 10 and 11both of which are coated with transparent coatings 12 and 13respectively which are electrically conductive (transparent conductorsor TC). These are further coated with two redox layers 14 and 15, atleast one of which has EC properties, which may also be referred to asEC2 and EC1 coatings respectively, assuming that both areelectrochromic. These coatings may be selected from inorganic materialsor comprise a polymeric matrix which itself is electrochromic or mayhave electrochromic additives. In one embodiment, the polymeric matrixmay be intrinsically conductive or have non-electronically conductivedyes along with electrically conductive nanoparticles (e.g., carbonnanotubes). These coated substrates are assembled together in a parallelconfiguration using an electrolyte layer 17 of uniform thickness whichmay be a prefabricated polymer film, or a liquid electrolyte or a liquidelectrolyte formulation at the time of assembly that is polymerizedafter introducing it into place between the two coated substrates. Theperimeter sealant to protect the electrolyte (17) and the EC1 (15) andEC2 (14) is shown as 18. Power is applied on the two opposing conductivesubstrates shown as 191 and 192 to change the optical properties. Whenthis VLTP is incorporated in an IGU, substrate 11 faces the outside ofthe building. EC1 and EC2 are considered as EC mediums VLTMs within theVLTP panel. When these prior-art panels are used to make windows andintegrated with IGUs, a large difference is observed between two suchwindows which are in different optical states and when these are viewedfrom the outside during the daytime. An example of an EC device withthis type of construction shown in FIG. 2a is in published US patentapplication 2020/0019032 (Agrawal, Jan. 16, 2020).

FIG. 2b shows another prior-art device where an electrolyte layer 17 acontaining EC materials may be used to form an EC medium (VLTM) insteadof the three layers 14, 15 and 17 in FIG. 2a . As in the prior devicethis may be a pre-fabricated film that is laminated, a liquid, or aliquid converted to a solid by polymerization after it is placed betweenthe coated substrates described below. For electrochromic devices, theseelectrolytes have at least one anodic and one cathodic dye (or they maybe bridged in a single molecule), for color control more than two dyesmay be used (for example, one cathodic dye and 2 to 5 or more anodicdyes, more than one bridged dye or bridged dye with additional anodic orcathodic dyes). In this figure clear substrates are shown as 10 a and 11a, and the transparent conductive coatings as 12 a and 13 a, sealant as18 a and the powering leads as 191 a and 191 b. In another variation aVLTP panel made of liquid crystalline material or a suspended particlemedium would also have the construction as shown in FIG. 2b where theVLTM 17a is replaced by a medium containing the liquid crystal or thesuspended particle material. In a thermochromic VLTP panel, notransparent conductors are required, and a film containing thermochromicVLTM would be laminated between the substrates 10 a and 11 a of FIG. 2b, but will not have the coatings 12 a and 13 a. In all of these types ofprior art panels, during daylight hours, differences are seen by casualobservers when the windows are in different states.

Other prior-art EC devices that have the same problem are made bysequentially depositing all of the layers as thin coatings on a singlesubstrate 11, which comprise of layer 13, 15, 17, 14 and then 12 (e.g.,see published US patent application 20140085701) after which anencapsulation layer may be deposited and/or this may be furtherlaminated using a polymeric film and a glass sheet to provide protectionto the coatings.

FIG. 3 shows a VLTP panel which has been integrated into an insulatingglass unit (IGU). The components 11-18 comprise an EC VLTP panel, andthe same numbering system is used as in FIG. 2a . The powering leads 191and 192 are not shown in FIG. 3 to simplify the drawing. The IGU is madeby assembling the VLTP panel 30 with another transparent substrate 32,typically glass which is coated with a low-e coating 33. These are puttogether using an edge (peripheral) spacer 31 a made out of metal orplastic which is bonded using adhesive 31 b. Desiccants are typicallyadded to these spacers. The gap 34 is evacuated or filled with a gassuch as air, argon, krypton, etc. If the cavity is evacuated, thenspacers are put throughout the cavity (not shown) so that the glass doesnot collapse due to the outside ambient air pressure. Typically, thisgap is about 2 mm or less when the cavity is evacuated, otherwise ittypically varies from about 5 to 20 mm when it contains a gas. The fourprincipal surfaces of this IGU are labelled from 1 through 4. Surface 1faces outside the building and surface 4 faces inside. Surfaces 3 and 2face the interior gap 34 of the IGU. There may be other variations inthe IGU construction, such as the low-e coating which is shown onsurface 3, may be deposited on surface 4 or surface 2. There may beadditional substrates which may be inserted in the gap 34 and they mayalso have a low-e coating, e.g., see FIGS. 7 to 9 in published US patentapplication 2020/0019032. In some literature, the surface of each panelof glass is numbered, for example, the interface between 15 and 17 being2, and then between 14 and 17 being 3 and so on, so that the surfacefacing the gap 34 is Surface 4 rather than Surface 2 as shown. However,in the surface convention used in this disclosure, the entire VLTPpanel, including any other films and laminates, is taken as a monolith,meaning that Surface 1 faces outside and Surface 2 faces the air (orgas) gap 34.

Also, the present disclosure includes embodiments in which the IGUs haveadditional panels in the air-gap (e.g., triple panel IGUs (which are notshown)). This means that there are two air or gas gaps on either side ofthis middle panel. These air gaps may be connected or both of them areisolated from each other. In addition, one of the surfaces (facing thegap) of the middle panel may also have a low-e coating, and in somecases the middle panel is quite thin (i.e., about or less than 1.7 mmdown to about 0.5 mm).

Diffused reflectance arises from paper or mediums with polymer dispersedliquid crystal media. Specular reflections arise from smooth metalcoatings and also when light travels from one clear medium to anotherclear medium with a different refractive index (RI). For example,unpolarized light traveling from air to standard clear-soda-lime glass(with an RI of 1.5) at normal incidence is reflected in an amount ofabout 4% and another 4% of the remaining light (3.84%) is reflected asit exits the other side into the air. Further, of the remaining lightbeing transmitted through the glass, 3.84% of light is reflected ofwhich 3.7% exits the front surface of the glass, making the totalreflection from the front substrate to be about 7.7%. This neglectshigher order reflections and absorption by glass. In this disclosure,unless mentioned otherwise refractive index (“RI”) always refers to thereal part of the refractive index “n” in the complex notation n+ik isused, “k” refers to light absorption and is related to tint.

For example, an IGU window unit constructed of two panels where one ofthem is a VLTP is shown in FIG. 3. Some proportion of the incoming lightfrom outside will be reflected from each surface/interface where thereis a change in refractive index and will contribute to the totalreflectivity.

When windows with VLTP elements are mounted on buildings, the solarlight striking these windows is reflected from not only the varioussurfaces and interfaces of the entire window, but may also be reflectedfrom the surfaces inside the building if these are bright (or highlyreflective) and are close to the window such as light colored drapes. Asubstantial amount of this light is transmitted back through the windowwith all reflected components contributing to the overall color andappearance.

When a window with prior-art VLTP element transitions from a clearer orlighter (bleached optical state) to a darker optical state, then thedarker state would largely block out the transmission of the reflectedlight coming from the inside glass element(s) of the IGU leading to asubstantial net reflectivity change (usually reduction) which may be inthe range of about 25 to 50% as discussed in more detail below. Inaddition, the color change will be further influenced by any of thereflected light passing towards the front (or to the outside of thebuilding) through the VLTM within the VLTP and taking the hue due to thelight absorbance of the VLTM as it passes through.

In a standard (prior art) IGU comprising a VLTP, the reflectivity isabout 14 to 16% when the VLTP is in the bleached or the clear state andit typically reduces to about 10% to 11% when the VLTP goes to a darkeststate. This means that there is a net reflectivity change of 29% whenthe reflectivity changes from 14% to 10% ((14−10)/14) or a netreflectivity change of 31% when the reflectivity change is from 16 to11% ((16−11)/16). Such net changes are substantial and result in avisible change in the appearance from outside when two windows arecompared in the two optical states. It is this net reflectivity changewhich needs to be reduced, and further any color change of the reflectedlight should be reduced, which may all be expressed as a change inreflected color.

In one embodiment, the front substrate of a VLTP which is present in anIGU and faces outside should reflect enough daylight from substrate 11,11 a in FIG. 2a, 2b or 3, so that this reflection dominates the humanperception as compared to the other reflections which originate from theinterior surfaces. This means that the product of the daylight intensitymultiplied by the reflectivity from this front substrate must exceed anyother reflected image when weighted by the photopic response of the eye.For computing the intensity of this image, a D65 illuminant source maybe used instead of daylight.

The advantages achieved by the invention of the present disclosureincludes use of a first glass substrate in the VLTP with certainreflectivity obtained from the coatings deposited on it. The firstsubstrate may be clear or permanently tinted (i.e. colored substrate).The desired reflectivity is achieved from this substrate and thereflective coatings stacked thereon, wherein the reflective coatingsstack comprises a number of transparent alternating coatings withdifferent refractive indices. This stack is also referred asinterference stack. The more intense outdoor light during the dayresults in a specular image of the outdoors (e.g., sky, outdoorlandscape and other buildings nearby). Further, the visible lightreflectivity of this coated substrate exceeds the specular reflectivityof any of the inboard substrates and coatings or coating stacks on thosesubstrates. To keep the figures simple, these coatings are collectivelyshown as a single coating as layer 26, 26 a and 26 b in FIGS. 4, 5 and 6respectively. In the devices with the reflective coating stack, thereflectivity in the bleached state will be higher which will lead tosmaller changes in net reflectivity. In one embodiment, the absolutereflectivity observed through the substrate where the coated side isfacing away from the light source for a combination substrate/reflectivestack/TC as compared to substrate/TC should be higher and in a range of4% to 25%. This means prior to constructing an EC device, if thisreflection is measured at 8% for Substrate/TC then forsubstrate/reflective stack/TC it should be in a range of 12% (8%+4%) to33% (25%+4%) in the same wavelength region. The reflection is typicallymeasured at equal intervals of wavelength (e.g., 5 nm) and then it issummed up in the desired range using the equation Σ(λ_(i)R_(i))/Σλ_(i).where at each wavelength λ_(i) the reflectivity is R_(i). Theinterference stack properties should be so selected such that it willlead to higher reflectivity from the surface of the VLTP panel or theIGU panel when observed from the outside. When this reflectivity ishigher, this dominates the visual perception of an outside observerregardless of the state of the optical coloration or the darkness of theEC medium. Thus, this change will also lead to lower net reflectivitychange in an IGU that contains the VLTP with the reflective stack.

In an embodiment, this reflectivity increase may be throughout thevisible spectrum or it can also acquire a certain color either caused bythe color of one or more of the coatings in the interference coatingstack and/or by further adding a substrate tint. The means that theoverall reflectivity from the substrate with the reflective layer willdecrease as some of the light will be absorbed by any permanent tints.However, the reflectivity has to be compared with the same substratetint but with and without the interference stack. This means that incertain embodiments, the above reflectivity numbers are not achieved inthe entire visible spectral range (from 380 to 740 nm) but rather in arange of narrow wavelength regions which have a range of about at least200 nm span, and in another embodiment this span is 100 nm. These rangesmay be contiguous or may comprise several regions adding up to the abovewavelength spans. For example, in the first case when the range is 200nm, the higher reflectivity may be in the wavelength range of 540-740nm; or in a second case higher reflectivity is between the range of 450to 550 nm and again between 580 to 680 nm again totaling 200 nm. Strongreflectivity even in a limited wavelength range masks minor reflectivitychanges at other wavelengths. Therefore, increased reflectivity of 4 to25% in the visible range would encompass increased reflectivity in awavelength range which is at least one of 100 nm, or 200 nm, or theentire visible range as discussed above.

When the interference layer itself uses one or more tinted layers, thenthe increased reflectivity is compared only for those wavelengths wherelight is not absorbed as long as the wavelength ranges are as specifiedabove. Tint in a transparent interference layer material is definedwhere its refractive index coefficient “k” in complex notation n+ik isequal to or more than 0.1 in the visible range (i.e., between 380 to 740nm) for at least in a span of 100 nm range within this visible region.Since, each of the films used in the interference layer are generallyless than about 100 nm, their “k” values have to be quite high toprovide appreciable tint. Clear coatings will have “k” less than 0.03 inthe visible region. When conflicting values of refractive index areavailable from different sources of a given material, the referencevalue must be that which is from the software “Essential Macleod”.

Permanent substrate tinting in one embodiment means that the substrateoptical transmission percentage should be reduced by at least 10% orlower compared to an equivalent thickness substrate. As a specificexample, the transmission of the non-tinted substrate and thepermanently tinted substrate (both of which are not coated and the samethickness), is measured at 400, 450, 500, 550, 600, 650 and 700 nm. If,at any of these wavelengths, the difference in percent transmission isgreater than 10, then the substrate is tinted, e.g., the non-tintedsubstrate may have a transmission of 80% at each of these wavelengths,and the tinted substrate will have to have a transmission of at least70% or less at any of these wavelengths. Permanent tint may also beadded by adding a colored reflective layer. Tinting the second substratethat forms the VLTP (substrate 10, 10 a in FIGS. 2a, 2b and 3 andsubstrate 20 in FIG. 4, etc.), may be useful for providing certainindoor light transmission characteristics, but is less impactful inreducing the change in reflectivity as observed from the outside. In oneembodiment, the front substrate is tinted, and its tint is similar tothe color that EC medium it contacts colors to, to further reduce thechange in reflectivity. Similar tint means that the peak opticalabsorption of the front substrate and the EC medium is within 50 nm ofeach other.

There are also restrictions (building codes) on the amount of lightwhich may be specularly reflected from the building (or automotive)glass as that may distract vehicle drivers nearby or create highintensity spots due to building's concave curvature. These restrictionsvary between different places and are also influenced by the buildingdesign (height, glass surface area, convex vs concave building shape,etc.), geographic orientation and the color of reflected light.

The RI of soda-lime glass, a most widely used glass substrate for avariety of building and automotive applications is about 1.525 at 550nm. The transparent materials (which may also have some color tint) forthe reflective stack are generally selected from metal oxides, metalnitrides, metal oxynitrides, metal carbides and metal oxycarbides. Themore preferred material choices are oxides, oxynitrides and nitrides.Some specific examples of these materials are SiO₂, Al₂O₃, SnO₂,fluorine doped SnO₂, In₂O₃, In₂O₃/SnO₂ (ITO), Sb₂O₅, TiO₂, Fe₂O₃, CoO,CuO, Mn₂O₃, ZnO, ZrO₂, Ta₂O₅, WO₃, NiO, Si₃N₄, SiO_(x)N_(y), TiN, andTiO_(x)N_(y) and mixtures of these. Also stoichiometries that deviatefrom the above may also be used and are represented by the abovecompositions. The thickness of each of the layers in a stack typicallyranges from about 10 nm to 100 nm of the different RI materials. RIdifferences amongst the coatings (or with the substrate) adjacent toeach other will typically vary in a range of about 0.35 to 1.4, inanother embodiment this range is 0.5 to 1.3, and in another embodimentthis range is 0.8 to 1.3. RI is dependent on wavelengths, and if notspecifically mentioned this is taken at 550 nm for comparison, as thatis close to the photopic vision. Thus, a soda-lime glass substrate maycomprise a reflective stack of coatings selected from a higherrefractive index material (e.g., tin oxide at 1.85, titania (TiO₂) at2.6, etc.) followed by a lower RI material, such as silica (SiO₂)(RI=1.46) and this sequence may be repeated with the same or differentthicknesses. The reflective stack is followed by a transparentconductor, which could be Indium/tin oxide or fluorine doped tin oxideas transparent conductors (RI in the range of about 1.85 to 2). Thus,the thickness of the transparent conductor (TC) will influence thereflectivity. Since the increasing thickness of TC increasesconductivity, the optimization of the stack will include a balance ofall properties. For some of the VLTPs as discussed above, a thin EClayer (less than 1,000 nm in thickness) may be deposited on thetransparent conductor. In this case, the influence of the EC layer alsoneeds to be considered on the reflectivity, which means that thereflective stack materials, thicknesses and/or number of layers willhave to be adjusted to get to a desired reflectivity.

Since the EC layer colors (or darkens) upon the application of voltage,the thin films of the EC materials deposited are preferably those wherethe change in the real part of the refractive index “n” is low. Anexample is tungsten oxide, in which “n” changes from 1.97 in the clearstate to 1.85 in the colored state (see Von Rottkay, K., et al, Opticalindices of electrochromic tungsten oxide, Thin Solid Films 306 (1997)p-10-16). Thus, the stack reflectivity prior to the light entering theEC medium will not change much when tungsten oxide colors.

The stack thicknesses and layering can be predetermined by knowing therefractive index of materials (both “n” and “k”) as a function ofwavelength in the visible spectrum, where “n” is the real part of therefractive index and “k” relates to the absorption component or theimaginary part in the complex number notation of refractive index. Manycompanies provide software for modelling optical properties of thesematerials, e.g., see “Essential Macleod” software from the Thin FilmCenter (Tucson, Ariz.). According to the present disclosure, colorimparting coatings may be used within the reflective stack to controlthe color of reflected light, colored coatings have an increasing “k”value in the wavelengths in which they absorb or are colored. Sometransparent coatings that can impart color from the above list areoxides containing, Fe₂O₃, CoO, CuO and Mn₂O₃ or using sub-stoichiometricoxides.

For those VLTPs which do not have a transparent conductor, thereflective stack is present on the inner side of the first (front)substrate that contacts the variable light transmission medium, such asa thermochromic film.

Although the reflectivity changes must be measured in complete EC (VLTP)panels, or after these are integrated within an IGU. However, the impactof change on reflectivity by coloring the EC layer deposited on asubstrate having a transparent conductor (TC) with and without areflective stack below the TC can be determined by making half cells.For example, taking the substrate 11 and coating it with the transparentconductor 13 and EC1 layer 15 (FIG. 2a ) and measuring the reflectivityfrom the uncoated side (e.g. see arrow in FIG. 2a ) both when the EC1layer is colored and it is bleached. The EC1 layer can be colored andbleached in a liquid electrolyte containing other passive electrodes andthen removing the substrates with EC1 for measurement. The same isrepeated for samples which are identical except that they have areflective stack below the transparent conductor. A minimum level ofcoloration in going from bleached to a colored state for a half cellwill be a light transmission ratio of at least 2.5 and in anotherembodiment at least 5 and yet in another embodiment 10. Depending on thecolor to which this material changes to, this could be at any wavelengthin the visible region, for tungsten oxide this may be selected as 550nm. These are not complete devices, however, they may be used to roughlyestablish a first level of viability, if the color change will cause thereflective change to be small, while at the same time the transmissivecolor change is large. This color change should be preferably measuredwhen the EC1 layer is in contact with a medium having a refractive indexsimilar to the electrolyte (see 17 in FIG. 2a ) being used. For example,this measurement may be made in contact with a liquid which is similarto the refractive index of the electrolyte. In most polymeric and liquidelectrolytes, this is in the range of about 1.4 to 1.55. Since the RI iswavelength dependent, the average numbers at 550 nm may be taken. Thereflectivity color change ΔE_(R)* in the two states should be less than6 in one embodiment, and less than 3 in another embodiment. Since thereflectivity difference from the coatings is being established, a blackbackground (light absorbing) should be used to measure this, otherwise,reflections from the background will interfere with this measurement.These small reflectivity changes are only defensible when these areaccompanied by large changes in transmission such as the numbers givenabove for half cells. The same measurements are then repeated for halfcells where a reflective stack is present below the transparentconductor.

For complete EC and other devices (or VLTP panels of any kind) thebleached state and the colored state are selected at the extreme rangeof their optical modulation which they would be exhibiting for a givenproduct.

FIG. 4 shows an EC VLTP construction according to the presentembodiments shown in FIG. 4. This figure shows a pair of transparentsubstrates 20 and 21 both of which are coated with transparent coatings22 and 23, respectively, which are electrically conductive (transparentconductors or TC). The reflective stack is represented by a single layer26 in FIG. 4, although this stack includes at least two or more layersas discussed earlier. These are further coated with two redox layers 24and 25, at least one of which has EC properties. In some embodiments,both have EC properties and may be referred to as EC2 (layer 24) and EC1(layer 25) coatings, respectively. These are assembled together in aparallel configuration using an electrolyte layer 27 of uniformthickness which may be a prefabricated polymer film. A perimeter sealant28 to protect the electrolyte and the EC1 and EC2 is shown. Power isapplied on the two opposing conductive substrates as shown as 29 a and29 b to change the optical properties. The reflective layer stack (26)increases the reflection of daylight and is termed as reflective orreflection enhancing layer(s). The present disclosure advantageouslyincludes selecting the coatings composition and their thicknesses sothat daylight is reflected from the first substrate (21) including thethin film stack (in this device this stack comprises layers 23, 25 and26). When the EC medium colors (e.g., layer 25 along with layer 24), theimpact on the amount of reflection or a change in its color is notnoticeable by an observer who is standing outside of the building andwatching the building under daylight conditions.

When an external observer views a building, which have VLTP panels invarious states of coloration, it is important that such differences arenot seen from outside. According to the present disclosure, thereflective color differences seen during daytime are as small aspossible. In one embodiment, these color differences measured as ΔE_(R)*are less than 8 for windows which are in different optical states,usually this is established by going the extreme of colored and bleachedstates and measuring the reflectivity. These changes may be measured inan IGU where such VLTPs are incorporated. In another embodiment, thiscolor difference ΔE_(R)* is less than 6, and in another embodiment lessthan 3. While the changes in the reflected color are small, the changein transmitted color and/or the optical transmission change at 550 nmmust be large. In one embodiment, the small changes in reflectivity ascharacterized above must be shown when the transmitted color change ofthe VLTP or the IGU that has these panels are large. The large colorchanges in transmission may be shown by ΔE_(T)* exceeding 40 and inanother embodiment exceeds 50 and in a further embodiment 60. In casethe transmission change is not measured by change in color but rather achange in transmission, the change in transmission ratio of the VLTPs orthe IGUs containing these VLTPs should be equal to or greater than 2.5at 550 nm (ratio of % transmission in bleached state divided and the %transmission in the colored state). 550 nm is typically used as itrepresents the peak of photopic response, i.e., eye sensitivity. Inanother embodiment the transmission ratio change is at least 5, and yetin another embodiment this ratio must change by at least 10.

In one embodiment as shown in FIG. 4, EC devices can be made with thesame reflected color and different transmitted color. In this device,the second EC layer 24 on the second substrate is separated from thefirst substrate 21 (and all of the coatings on it) using a thickelectrolyte layer 27 (thickness greater than 10 μm). This separationeliminates interference of the reflections coming from these substrates,which means that the light coming from the second EC layer (transmittedor reflected) will not cause any coherent optical interference from thelight being reflected from the front substrate and also will be muchlower in intensity as compared to the high reflectivity emanating fromthe front substrate.

Another way of achieving this is shown by a different type of an ECdevice as shown in FIG. 6. FIG. 6 shows an EC device incorporated intoan IGU. IGU is formed another clear substrate 32 that has a low-ecoating 33. The EC device 30 b and the substrate 32 are separated by agap 34 which is filled with a gas as discussed earlier. 31 a is aperipheral spacer gasket that keeps the substrates apart and is bondedin place by an adhesive 31 b. The device comprises two clear substrates20 b and 21 b, where 21 b is coated with a reflective stack 26 bfollowed by a TC 23 b. Substrate 20 b is coated with a TC 22 b and theseare then assembled in a parallel configuration where the TC coatingscontact a thick electrolyte (typically greater than 10 microns inthickness). 28 b is a perimeter sealant. The electrolyte is also anelectrochromic medium as this has redox dyes. Since, the reflectivelayer increases the reflectivity prior to the light entering the ECmedium, these devices also show reduced color change in reflection asthe EC device colors. In many IGUs, it is desirable that substrate 32 istempered for increasing strength and safety so that if the glass were tobreak, injuries to the occupants are minimized as tempered glass breaksin small pieces without having sharp corners. This is particularly donefor windows which are placed in commercial buildings and also inresidential buildings in swinging windows and in doors (that is for thewindows that are present in the doors). Further, tempering may also beperformed for the VLTP (or EC in this case) forming glasses like 11 or11 and 10 so that the chances of window breakage is minimized in casethese windows heat-up due to large absorption of the solar radiation(which gets converted to heat, particularly when the VLTP element is inthe dark state).

Another way of forming a high efficiency EC device for single panewindows or automotive glass is to bond a film with a low-e surface on tothe inside facing surface of an EC panel. These films may be on polymersubstrates. As an example, the films should have a low-e coating withemissivity of 0.2 or lower in one embodiment and 0.1 or lower in anotherembodiment. Typically a low emissivity of as low as 0.02 may be achievedon these films. For example, low-e may include a low emissivity of 0.3to 0.01 in one aspect, or 0.2 to 0.02, or any number or range within thedisclosed ranges. These films may be polymeric or non-polymeric and mayhave an adhesive for bonding. Ecolux™ 70 from Saint Gobain PerformancePlastics (San Diego, Calif.) and Thinsulate™ Climate Control 75™ from 3M(St. Paul Minn.) are polyester films with a low-e coating. For some ECproducts a UV protective film may be applied on the outside surface ofthe EC panel. Examples are Sentinel Plus OX 80, Sentinel Plus OX 50,Sentinel Plus SS 45, SX80, SX50, SS45 and SS25 all from Saint GobainPerformance Plastics; Prestige Exterior 90, Prestige Exterior 70,Prestige Exterior 50, Prestige Exterior 40, Prestige Exterior 20, SafetyS70 Exterior from 3M; and Exterior Bronze 35 from XPEL Technologies (SanAntonio, Tex.).

For a given EC device (for example, the type of tint on the frontsubstrate, the type of interference layer or its absence, the type of ECmaterial (i.e., its color in the bleached and colored states), theselection of the low-e glass is highly important in ensuring that theΔE_(R)* is not compromised. For an IGU comparing a VLTP panel, in firstembodiment, the ΔE_(R)* should be about equal to or less than 3, 6 or 8(as discussed earlier in three embodiments), and in second embodimentthe selection of low-e glass should be made so that the increase invalue of ΔE_(R)* should not be more than 2 when the EC panel isintegrated into the IGU and in third embodiment this should not be morethan 4. As an example, according to the second embodiment, if theΔE_(R)* of the EC panel from the colored to the bleach state is 2, thenthe ΔE_(R)* of the IGU should not exceed 4 upon coloration of the ECdevice; and according to the third embodiment this number would be 6. Inthose window applications where IGU constructions are not used the abovenumber apply for the EC panels, or EC panels with UV blocking orsolar-light modulating films, and/or films with low-e surfaces. In thiscase the reflectivity for establishing color difference from outside ismeasured from the surface of the VLTP panel or the film surface thatfaces outside.

In another embodiment both ΔE_(R)* and ΔE_(R-H)* are considered. TheΔE_(R)* considerations are listed above, and in this embodimentΔE_(R-H)* are added and this should be equal to or less than 4 for theEC panel or the IGU.

Examples of EC devices where thick electrolytes are used and also havean EC layer 24 are provided in U.S. Pat. No. 6,853,472 and published USpatent applications 2020/0019032, 2020/0017648, 2019/0196291 and2014/0205748. The first two published applications describe deviceswhere the EC layer 24 comprises of conductive particles and dyes(typically organic and organometallic redox dyes with EC properties) andEC layer 25 can be a thin inorganic coating of an EC material, such astungsten oxide containing material. The dyes in EC layer 24 may beselected to provide different colors. Examples of dyes in theelectrolyte (such as those described in FIG. 2b ) can be found in U.S.Pat. No. 6,141,137 (Byker), where several anodic and cathodic dyes areincorporated into a thick electrolyte.

FIGS. 4, 5 and 6 show the EC devices formed using the present inventionand their incorporation in the IGU. There may be other ways ofconfiguring the substrate with the transparent conductor (TC) that facesthe outside and achieve the color aspects as discussed herein. These areshown in FIGS. 7a-7e . These embodiments will be discussed in referenceto FIG. 4 which shows an EC device or the VLTP panel (without the IGU).FIG. 7a shows the structure of the outside glass used to form the ECdevice as in FIG. 4. This means that the outside glass in FIG. 4 shownas 21, interference layer 26 and the transparent conductor 23 arerespectively similar to 71, 76 and 73 shown in FIGS. 7a-7e . The EClayer or the EC medium or any VLTP medium contacts the transparentconductor (TC). To form a VLTP device, a VLTP medium contacts surfaceshown as 79 b (FIGS. 7a -7 e). In FIG. 4, the EC medium “EC1” isdeposited or contacts the transparent conductor 23. As usual, the thickarrow shows the outside facing surface of the device.

The other variations shown in FIGS. 7b-7e will be explained in referenceto FIG. 7a . In order to keep the labelling consistent in all of thesefigures, label 73 always is the transparent conductor (TC) whichcontacts the VLTP medium, 71 is the substrate on which the transparentconductor 73 is deposited, and the interference layer to provide thereflectivity when present is shown as 76. It is to be understood thatfor each case the characteristics of the interference layer or the colorof the layer may have to be fine-tuned to get the desired effects, inother words, the characteristics of the interference layer(s) (i.e., ifthe interference layer comprises of multiple layers) if optimized forthe embodiment shown in FIG. 7a may not be optimum for FIG. 7b and soon. Even if the same materials are used to form these layers theirthicknesses and colors may be different to get an equivalent amount ofreflectivity and color.

FIG. 7b shows that the substrate 71 and the TC is shown as 73, which islaminated to another substrate 77, wherein the latter has theinterference layer 76 deposited on it. The lamination material 78 istypically a polymeric film (also called an interlayer) which may be madeout of clear copolymers. Some examples of these copolymer films arefluoropolymers, thermoplastic polyurethane, polyvinyl butyral (PVB),acrylic, polyester, polyurea, polycarbonate, polyvinyl acetate, orcombinations thereof. The light absorption and reflectioncharacteristics and the thicknesses of the materials 77, 76, 78 and 71may be adjusted which result in the desired reflectivity. In general,the interlayer thickness is from about 100 to about 2,000 μm. Avariation of this theme is where the reflective stack 76 is deposited onthe substrate 71 so that it contacts the interlayer 78. In anothervariation of this theme, substrate 77 may be rigid (e.g., glass) or maybe a polymeric film which is flexible and generally in a range of about25 to 250 μm in thickness. In case a flexible film such as polyester orpolycarbonate is used with an interference layer 76, the interlayer 78may be replaced by an adhesive layer (e.g., a pressure sensitiveadhesive) that is formed on top of the interference layer and protectedby a release film. This release film is removed prior to bonding thisassembly on the surface of 71. The use of a flexible film also providesthe capability to use the reflective properties for retrofitapplications.

In FIG. 7c , the interference layer 76 is deposited on the first side ofthe substrate 71, since TC is deposited on the second side. In this caselayer(s) 76 are not protected from the elements and may include a hardor a weather/scratch-resistant coat.

FIG. 7d shows another variation where the interference stack 76 isdeposited on a substrate 75 (third substrate). This substrate may berigid (e.g., glass) or a flexible polyester or polycarbonate film asdiscussed earlier. This is laminated using two interlayers 78 and 79between the substrates 71 (first substrate) and 77 (second substrate).In a further variation of this theme, the interference stack 76 may bedeposited on any side of the third substrate 75, that is facing thesubstrate 77 (which is shown) or facing substrate 71. In anotherembodiment, a flexible substrate 75 with an interference layer may alsobe used, where one side of this film has an adhesive layer, i.e.,equivalent to layer 78 to bond to substrate 71 and is then laminatedusing a film 79 to the substrate 77.

FIG. 7e shows another variation where substrate 77 is laminated tosubstrate 71 using an interlayer 78 (or layer 78 is an adhesive layer).The color of the interlayer, adhesive or the substrate 77 is selected sothat the impact of the reflected light coming from the EC device is low.In this case, typically the color of one of these is intense so that thetransmission of the visible light through the stack shown in FIG. 7e isless than about 50%.

In another embodiment, at least one of the interlayers or the adhesivesor the flexible (polymeric) film used in the embodiments or togetherwhen used together has high UV blockage. This means that the opticalabsorbance of the radiation in the wavelength range of 290 to 390 nmshould be at least two (this also means that UV in this range isattenuated by 99%). In another embodiment this range is extended fromabout 290 nm to 400 nm. Yet in another embodiment the UV is attenuatedin the range of 290 to 400 nm by at least 90%. (optical absorbance of 1)This attenuation is measured at any wavelength in the stated regions.For example, such laminating interlayers of PVB are available as Saflex™and Saflex™ UV (Eastman, Kingsport, Tenn.); PVB (Trosifol™, Trosifol™ UVExtra Protect) and ionoplast interlayers (Sentryglas®) from Kurraray,Japan; UA01 UB03 from Sekisui Chemicals. Flexible polyester films withpressure sensitive adhesives in different colors, reflection,transmission and Low-e surfaces are available for example from SaintGobain (Malvern, Pa.), 3M (St. Paul, Minn.) and XPEL Technologies (SanAntonio, Tex.) for a variety of applications related to the buildingsand transportation.

Even though buildings may have VLTP panels, these may be supplemented byblinds, which may be used to reduce the direct solar glare at certaintimes during the day or to provide privacy at night by changing a clearvision to a hazy or a translucent vision by scattering light. Dependingon the color, these blinds may still reflect quite a bit of the incominglight from the outside. Thus, it is preferred that the drape color (orthe side of the drape facing the window) should be darker in color.These drapes may be integrated within the IGUs so that they are placedwithin the air/gas space of an IGU such as in the region 34 of FIGS. 3,5 and 6. For example, drapes integrated with passive IGU window unitsare available as Blink™ from ODL (Zeeland, Mich.). These drapes may alsobe outside the IGUs to mitigate the above situations.

These drapes (e.g., roller shades) may be woven or knitted structureshaving an openness factor between 0.5 and 10%, and in another embodimenthaving an openness factor between 2 to 5% and in another embodimentbetween 5 and 10%. Such fabrics for drapes will be collectively termedas open fabrics or as sheer fabrics. The visible light transmittance ofthese fabrics may range from 2 to 25% and in another embodiment between5 to 20%. The solar transmission is in the range of 10-30% and solarreflection in the range of 30 to 70%. The solar transmission, reflectionand the visible transmission properties may be determined using testmethod EN14500:2008 (test method available from SAI Global Standards,Chicago, Ill.). Since light color fabrics result in maximum contrastwhen drawn, it is important to test the impact of light-colored shadeson the VLTP window systems. A preferred color of these fabrics fordrapes that are not visible from outside are darker with L* values below30. The drapes may also have dark colors that face outside and light,white and off-white colors (L value >70) facing inside. The same may beused for drapes placed within the gas space of the IGU as describedearlier. Both light and dark fabrics can reduce direct solar glarecombined with the transmission change of the VLTP panels. The lightcolored drapes provide superior privacy and the dark colored drapesprovide superior vision to the outside view. More details on fabrics andtheir use to block glare and provide privacy is found in KONSTANTZOS,Iason, et.al., Daylight Glare Evaluation when the Sun is Within theField of View Through Window Shades, Proceedings of 4th InternationalHigh Performance Buildings Conference at Purdue, Jul. 11-14, 2016(Purdue e-Pubs, Purdue University, West Lafayette, Ind.).

The present disclosure includes the following non-limiting aspects:

Aspect 1. An electrochromic variable light transmission panel (VLTP)comprising:

-   -   (a) a first transmissive substrate and a second transmissive        substrate arranged in a parallel configuration;    -   (b) wherein the first transmissive substrate comprises a first        side and a second side, wherein the second side of the first        substrate is coated with a coating stack comprising at least two        layers, followed by a coating of a transparent conductor and        further followed by an electrochromic (EC) layer;    -   (c) and an electrolyte layer disposed between the first and        second transmissive substrates, wherein the electrolyte layer        contacts the said EC layer;    -   wherein the said VLTP shows a color difference ΔE_(T)* of        greater than 40 in transmitted color when measured in the        bleached and the colored optical states, and shows a color        difference ΔE_(R)* of less than 6 when measured in the bleached        and the colored optical states when reflection is viewed from        the first side of the first substrate.        Aspect 2. The electrochromic VLTP as in aspect 1, wherein the        ΔE_(R)* is less than 3.        Aspect 3. The electrochromic VLTP as in aspect 1, wherein a        second transparent conductor layer is deposited on the second        substrate followed by a layer of a second EC material, wherein        the second EC material contacts the said electrolyte.        Aspect 4. The electrochromic VLTP as in aspect 1, wherein the        coating stack comprises materials which have different        refractive indices        Aspect 5. The VLTP in aspect 3, wherein the composition of the        second EC material deposited on the second transmissive panel is        selected from an inorganic metal oxide and a polymeric        composition.        Aspect 6. The VLTP in aspect 5, wherein the polymeric        composition comprises electrically conductive nanoparticles.        Aspect 7. An insulated glass unit (IGU) assembly comprising the        VLTP of aspect 1, wherein the said IGU assembly contains at        least one low-e coated panel in addition to the said VLTP; and        the said IGU assembly shows a color difference ΔE_(T)* of        greater than 40 in transmitted color when compared in the        bleached and the colored optical states of the VLTP, and shows a        color difference ΔE_(R)* of less than 8 when reflection is        viewed from the first side of the VLTP when compared in the        bleached and the colored optical states of the VLTP.        Aspect 8. The VLTP as in aspect 1, wherein ΔE_(T)* is less than        4.        Aspect 9. A IGU assembly as in aspect 7, wherein ΔE_(T)* is less        than 4.        Aspect 10. A window comprising the VLTP of aspect 1, further        comprising a film bonded to the second substrate on the side        that is not facing the electrolyte layer, and the said film has        a low-e surface.        Aspect 11. An electrochromic variable light transmission panel        (VLTP) comprising    -   (a) a first transmissive substrate and a second transmissive        substrate arranged in a parallel configuration;    -   (b) wherein the first transmissive substrate comprises a first        side and a second side, wherein the second side is coated with a        stack of coatings comprising at least two layers, followed by a        coating of a transparent conductor;    -   (c) wherein the second transmissive substrate comprises a first        side and a second side, wherein the first side of the second        transmissive substrate is coated with a transparent conductor;    -   (d) wherein the substrates are disposed in an assembly such that        an electrochromic medium is disposed between sides coated with        the transparent conductors on the two substrates;        wherein the said VLTP shows a color difference ΔE_(T)* of        greater than 40 in transmitted color when measured in the        bleached and the colored optical states, and shows a color        difference of ΔE_(R)* of less than 6 when reflection is viewed        from the first side of the first substrate.        Aspect 12. The VLTP of aspect 11, wherein the electrochromic        medium is an electrolyte which has electrochromic properties        Aspect 13. The VLTP of aspect 11, wherein at least one        electrochromic coating is deposited on one of the said        transparent conductors.        Aspect 14. The VLTP as in aspect 11, wherein ΔE_(T)* is less        than 4.        Aspect 15. A window comprising a VLTP of aspect 11, further        comprising a film bonded to the second side of the second        substrate, wherein the said film has a low-e surface.        Aspect 16. The VLTP in aspect 11, wherein the composition of the        EC layer deposited on the second transmissive panel is selected        from an inorganic metal oxide and polymeric composition.        Aspect 17. An insulated glass unit (IGU) assembly comprising the        VLTP of aspect 11, wherein the said IGU assembly comprises at        least one low-e coated panel in addition to the said VLTP; and        the said IGU assembly shows a color difference ΔE_(T)* of        greater than 40 in transmitted color when compared in the        bleached state and the colored optical states of the VLTP, and        in these optical states of the VLTP, the IGU assembly shows a        color difference in reflected color ΔE_(R)* of less than 8 when        reflection is viewed from the first side of the VLTP.        Aspect 18. The IGU assembly as in aspect 16, wherein ΔE_(R-H)*        is less than 4.        Aspect 19. An electrochromic variable light transmission panel        (VLTP) comprising    -   (a) a first transmissive substrate and a second transmissive        substrate arranged in a parallel configuration;    -   (b) wherein the first substrate comprises a first side and a        second side, wherein the second side is coated with a stack of        coatings comprising at least two layers, followed by a coating        of a transparent conductor;    -   (c) wherein the second substrate comprises a first side and a        second side, wherein the first side of the second substrate is        coated with a transparent conductor;    -   (d) wherein the substrates are configured in an assembly such        that an electrochromic medium is disposed between conductive        sides of the first and second substrates;        wherein the said VLTP shows a transmission ratio of greater than        2.5 at 550 nm when measured in the bleached and the colored        states, and, in these optical states, shows ΔE_(R)* of less than        6 when reflection is viewed from the first side of the first        substrate.

Aspect 20. the electrochromic VLTP as in aspect 19, wherein theelectrochromic medium has electrolytic properties.

Aspect 21. The electrochromic VLTP as in aspect 19, wherein the firstsubstrate comprises soda-lime glass and the stack of coatings comprisesat least two of SiO₂, Al₂O₃, SnO₂, Sb₂O₅, TiO₂, Fe₂O₃, CoO, CuO, Mn₂O₃,ZnO, ZrO₂, Ta₂O₅, Si₃N₄, SiO_(x)N_(y), TiN, and TiO_(x)N_(y), andmixtures thereof, and wherein each of the two layers in the stackcomprises at least one of SiO₂, Al₂O₃, SnO₂, Sb₂O₅, TiO₂, Fe₂O₃, CoO,CuO, Mn₂O₃, ZnO, ZrO₂, Ta₂O₅, Si₃N₄, SiO_(x)N_(y), TiN, andTiO_(x)N_(y).

Aspect 22. The electrochromic VLTP as in aspect 19, wherein a layer inthe stack that contacts the first substrate has a higher refractiveindex as compared to the first substrate.Aspect 23. The electrochromic VLTP as in aspect 19, wherein each layerin the stack has a thickness of 5 to 100 nm.Aspect 24. The electrochromic VLTP as in aspect 19, wherein

-   -   a) the first substrate is tinted,    -   b) at least one of the coatings in the stack is tinted, or    -   c) both a) and b).        Aspect 25. An insulated glass unit (IGU) assembly comprising at        least one low-e coated panel and a VLTP separated by a gap,        wherein the VLTP comprises:    -   (a) a first transmissive substrate and a second transmissive        substrate arranged in a parallel configuration;    -   (b) wherein the first substrate comprises a first side and a        second side, wherein the second side is coated with a coating        stack comprising at least two layers, followed by a coating of a        transparent conductor and further followed by a EC layer;    -   (c) and an electrolyte layer disposed between the first and        second substrates, wherein the electrolyte layer contacts the        said EC layer;    -   wherein the said IGU assembly shows a color difference ΔE_(T)*        of greater than 30 in transmitted color when compared in the        bleached and the colored optical states of the VLTP, and in        these optical states, shows a color difference ΔE_(R)* of less        than 8 when reflection is viewed from the first side of the        first substrate.        Aspect 26. An insulated glass unit (IGU) assembly comprising at        least one low-e coated panel and a VLTP separated by a gap,        wherein the VLTP comprises    -   (a) a first transmissive substrate and a second transmissive        substrate arranged in a parallel configuration;    -   (b) wherein the first transmissive substrate comprises a first        side and a second side, wherein the second side is coated with a        stack of coatings comprising at least two layers, followed by a        coating of a transparent conductor;    -   (c) wherein the second transmissive substrate comprises a first        side and a second side, wherein the first side is coated with a        transparent conductor;    -   (d) wherein the first and second substrates are configured in an        assembly such that an electrochromic medium is disposed between        conductive sides of the first and second substrates;    -   and the said IGU assembly shows a color difference ΔE_(T)* of        greater than 30 in transmitted color when compared in the        bleached and the colored optical states of the VLTP, and, in        these optical states, shows a color difference ΔE_(R)* of less        than 8 when reflection is viewed from the first side of the        first substrate.        Aspect 27. A method of making an electrochromic variable light        transmission panel (VLTP) having a color difference ΔE_(T)* of        greater than 40 in transmitted color when measured in the        bleached and the colored optical states, and a color difference        ΔE_(R)* of less than 6 when measured in the bleached and the        colored optical states when reflection is viewed from the first        side of the first substrate, comprising:

providing a first and a second transmissive substrate, each having afirst side and a second side, respectively, and arranged in a parallelconfiguration so that the second side of the first transmissivesubstrate faces the first side of the second transmissive substrate;

coating at least two coating layers on the second side of the firsttransmissive substrate;

coating a first transparent conductor layer over the at least twocoating layers; and

coating a second transparent conductor on one side of the secondtransmissive substrate

disposing an electrochromic material between the two transparentconductors.Aspect 28. The method of aspect 27, wherein the said electrochromicmaterial is dispersed in an electrolyte, and the said electrolytecontacts the two transparent conductors.Aspect 29. The method of aspect 28, further comprising an EC layerdeposited on the transparent conductor of the first substrate.Aspect 30. The method of aspect 29, further comprising: coating a secondtransparent conductor layer on the first side of the second substrate,followed by coating a second EC layer over the transparent conductorlayer on the second substrate, wherein the second EC material contactsthe electrolyte layer.Aspect 31. The method of aspect 27, further comprising: bonding a low-efilm to the second side of the second substrate.Aspect 32. The method of aspect 27, wherein the EC layer is disposed inthe VLTP as a prefabricated polymer film.Aspect 33. The method of aspect 27, wherein the ΔE_(R)* is less than 3.Aspect 34. The method of aspect 27, wherein the first substratecomprises soda-lime glass and the at least two coating layers areindependently selected from SiO₂, Al₂O₃, SnO₂, Sb₂O₅, TiO₂, Fe₂O₃, CoO,CuO, Mn₂O₃, ZnO, ZrO₂, Ta₂O₅, Si₃N₄, SiO_(x)N_(y), TiN, andTiO_(x)N_(y), and mixtures thereof.Aspect 35. The method of aspect 34, wherein one or both of the at leasttwo layers coated on the first substrate has a higher refractive indexas compared to the first substrate.Aspect 36. The method of aspect 27, wherein each layer in the at leasttwo coating layers independently has a thickness of 5 to 100 nm.Aspect 37. The method of aspect 27, wherein at least one of the firstsubstrate and one of the coatings in the at least two coating layers istinted.Aspect 38. The method of aspect 27, further comprising: providing anadditional transparent panel arranged in a parallel configuration to theVLTP and separated by a gap.Aspect 39. The method of aspect 38, wherein the additional transparentpanel comprises a glass substrate coated with a low-e coating.Aspect 40. The method of aspect 38, wherein the gap between theadditional transparent panel and the VLTP is spaced apart by a spacer.Aspect 41. The method of aspect 38, wherein the gap is evacuated orfilled with a gas selected from air, argon, or krypton.Aspect 42. The method of aspect 41, wherein the additional transparentpanel and the VLTP comprise an insulated glass unit (IGU), and whereinthe VLTP is configured to face outside of a building.Aspect 43. The method of aspect 40, wherein the spacer comprises amaterial selected from metal or plastic.Aspect 44. The method of any one or combination of aspects 38-43,wherein the gap is in the range of 2 mm to 20 mm.Aspect 45. The method of aspect 39, wherein the low-e coating isdisposed on the side of the additional transparent panel facing theVLTP.Aspect 46. The method of aspect 42, wherein the IGU shows a colordifference ΔE_(T)* of greater than 30 in transmitted color when comparedin the bleached and the colored optical states of the VLTP, and, inthese optical states, shows a color difference ΔE_(R)* of less than 8when reflection is viewed from the first side of the first substrate.

EXAMPLES

All of the optical modelling reported in the following examples wascarried out by using “Essential Macleod” software obtained from the ThinFilm Center in Tucson, Ariz. Unless reported otherwise all of therefractive index data were obtained from the libraries in this software.In this example, the impact on optical reflectivity was modelled byintroducing an interference stack comprising of a two-layer stack ofTiO₂ and SiO₂; Si₃N₄ and SiO₂; and a four-layer stack ofTiO₂/SiO₂/TiO₂/SiO₂. All of these coatings are optically clear, and allof the substrates used were also clear, i.e., were not tinted. Theinterference stack was introduced between the glass substrate (soda-limeglass) and the transparent conductor ITO in a thickness of 120 nm.Unless mentioned otherwise, the RI properties of the polymer used(Table 1) in all of the modelled examples is the same. We found that inthe modelling the impact of change in the polymer refractive index insteps down to average value of 1.4 (from the one used with an averagevalue of 1.55), had a minor impact on the results with no changes intrends which are discussed below.

TABLE 1 Refractive index of Polymer Wavelength, nm 400 450 500 550 600650 700 RI 1.5708 1.5601 1.5545 1.5499 1.5485 1.5466 1.5452

In all of the examples with modelling results (Examples 1 through 4),only half cells were modelled to observe the changes possible to thereflectivity coming from the front substrates and an EC medium incontact with it. In Examples 2 to 3, a thin EC film of tungsten oxidewas used that contacted the TC on the front substrate i.e., substrate 21a, interference stack 26 a, TC 23 a and the EC medium 25 a in contactwith a polymeric medium 27 a which is a thick electrolyte (see FIG. 5).28 a is a perimeter sealant. In Example 4, the configuration of the EChalf-cell resembles to the one shown in FIG. 6 which is substrate 21 b,interference stack 26 b, TC 23 b and the thick EC medium 27 b, which isalso an electrolyte.

Example 1: Reflectivity Change by Incorporation of an Interference Stack

The sequence of the modelled stacks is shown in Table 2. Thereflectivity was modelled from the glass side. As seen, there is aconsiderable increase in reflectivity at all wavelengths when theinterference stack was introduced

TABLE 2 Change in reflectivity by introducing interference stack(TiO₂(45 nm)/SiO₂(35 nm)/) Glass/TiO₂(45 nm)/ Glass/ITO(120 nm)/ SiO₂(35nm)/ Wavelength polymer ITO(120 nm)/polymer (nm) % T % R % T % R 40087.8 8.2 72.8 23.5 450 91.6 4.8 77.7 19.1 500 92.2 4.7 75.4 22.0 55091.8 5.5 77.3 20.4 600 91.4 6.1 81.7 16.1 650 91.4 6.3 85.8 12.0 70090.0 5.8 86.5 9.3

Example 2: Impact of Interference Stack on the Transmission Color andReflected Color of a Substrate with Electrochromic Tungsten Oxide

In this example the substrates from Example 1 were further modelled byincorporating a 400 nm thick tungsten oxide. The change in color intransmission was modelled using the colored and the bleached state oftungsten oxide. The RI values in the two states for tungsten oxide wereobtained from Von Rottkay, K., et al (1997). The results in Table 3 showthat in both cases (with and without the interference layers) thetransmission color change due to the changes in the optical propertiesof tungsten oxide is large and similar at 40.9 and 41, whereas there isa large reduction in reflected color from 19.3 to 9.2 when theinterference layer was incorporated. All of these calculations were doneat normal angle.

TABLE 1 Impact of reflectivity at normal angle w and w/o stackTransmission Transmision Reflectance Reflectance Bleached ColoredBleached Colored L* a* b* L* a* b* L* a* b* L* a* b* Sample (T) (T) (T)(T) (T) (T) ΔE_(T)* (R) (R) (R) (R) (R) (R) ΔE_(R)* Glass/ITO(120 nm)/96.0 −1.4 1.7 57.0 0.7 −10.3 40.9 32.0 5.3 −4.2 17.7 −3.2 5.6 19.3WO3(400 nm)/ polymer Glass/TiO2(45 nm)/ 92.7 0.8 9.2 54.4 1.8 −5.5 41.045.7 −3.5 −20.9 41.1 −11.2 −18.9 9.2 SiO2(35 nm)/ ITO(120 nm)/WO3 (400nm)/polymer

Table 4 lists the transmission and reflectivity changes as a function ofthe wavelength. This table shows that the change in reflection averagedat all wavelengths is higher both in the colored and in the bleachedstate when the interference stack is introduced, respectively, and thechange in relative reflectivity at 550 nm is 56.5% ((6.9−3)/6.9) whenthe stack is not present and 35% ((19.8−12.8)/19.8) when the reflectivestack is present.

TABLE 4 Percentage Transmission and reflection of WO3 coating with andwithout interference stack Glass/ITO(120 nm)/WO3 Glass/TiO₂(45nm)/SiO₂(35 nm)/ITO(120 nm)/ (400 nm)/polymer WO3(400 nm)/polymerWavelength Bleached Colored Bleached Colored (nm) % T % R % T % R % T %R % T % R 400 78.8 11.7 29.1 1.9 52.9 40.4 22.8 22.8 450 87.8 8.1 32.52.2 63.8 33.1 26.5 20.1 500 90.2 6.5 28.2 1.4 85.2 11.6 23.3 18.5 55090.2 6.9 24.6 3.0 77.7 19.8 22.1 12.8 600 88.7 8.4 23.1 2.4 90.4 6.722.2 6.3 650 92.2 5.2 22.7 1.3 83.4 14.3 21.7 5.8 700 91.1 4.8 22.3 0.880.2 16.1 21.1 6.2

Table 5 shows the calculations for the same stack at normal angle and at30 degrees (off-normal angle). These results show that the difference inthe bleached and the colored states at both angles is small, i.e., 9.2vs 10.3, the relative difference between the two is 12%((10.3−9.2)/9.2).

TABLE 5 Normal and off-angle comparison of color for Glass/TiO₂(45nm)/SiO₂(35 nm)/ITO(120 nm)/WO₃(400 nm)/polymer Normal Angle Off angle(30°) Reflectance Reflectance Reflectance Reflectance Bleached ColoredBleached Colored L* a* b* L* a* b* L* a* b* L* a* b* (T) (T) (T) (T) (T)(T) ΔE_(R)* (R) (R) (R) (R) (R) (R) ΔE_(R)* 45.7 −3.5 −20.9 41.1 −11.2−18.9 9.2 30.1 9.9 −17.6 28.1 1.5 −23.2 10.3

Example 3: Impact of Interference Stack where TiO₂ is Replaced by Si₃N₄on the Transmission and Reflection Properties of a Substrate withElectrochromic Tungsten Oxide

In this example, Si₃N₄ was substituted for TiO₂ in the interferencestack. Table 6 shows that the reflectivity level achieved is higher whenTiO₂ is used, although the use of Si₃N₄ also enhances the reflectivityas compared to the situation when no stack is used (see Table 4 for datawith no stack).

TABLE 6 Comparison of Si3N4 Vs TiO2 in the interference stackGlass/TiO2(45 nm)/SiO2(35 nm)/ITO Glass/Si3N4(45 nm)/SiO2(45 nm)/ITO(120 nm)/WO3(400 nm)/polymer (120 nm)/WO3(400 nm)/polymer WavelengthBleached Colored Bleached Colored (nm) % T % R % T % R % T % R % T % R400 52.9 40.4 22.8 22.8 62.4 30.0 25.9 12.6 450 63.8 33.1 26.5 20.1 72.923.7 29.3 11.8 500 85.2 11.6 23.3 18.5 89.8 6.9 25.5 10.8 550 77.7 19.822.1 12.8 82.7 14.6 23.2 8.3 600 90.4 6.7 22.2 6.3 91.9 5.1 22.9 3.1 65083.4 14.3 21.7 5.8 88.9 8.6 22.5 2.2 700 80.2 16.1 21.1 6.2 84.9 11.221.9 2.4

Table 7 compares the change in color for these two cases. It is seenthat although there is not much difference in color comparing thebleached state and the colored state in transmission (ΔE_(T)* values are41.0 and 41.4) but the use of titanium oxide is able to suppress thecolor change in reflection more effectively as seen by the ΔE_(R)*values. These color values without stack are in Table 3.

TABLE 7 Comparison of color change when Si3N4 and TiO2 are used in thestack Normal Angle Transmission Transmission Reflectance ReflectanceBleached Colored Bleached Colored L* a* b* L* a* b* L* a* b* L* a* b*Sample (T) (T) (T) (T) (T) (T) ΔE_(T)* (R) (R) (R) (R) (R) (R) ΔE_(R)*Glass/TiO2(45 nm)/ 92.7 0.8 9.2 54.4 1.8 −5.5 41.0 45.7 −3.5 −20.9 41.1−11.2 −18.9 9.2 SiO2(35 nm)/ ITO(120 nm)/WO3 (400 nm)/polymerGlass/Si3N4(45 nm)/ 94.5 0.3 6.3 55.7 1.7 −7.7 41.4 39.0 −2.5 −18.6 32.2−14.2 −14.6 14.1 SiO2(45 nm)/ ITO(120 nm)/WO3 (400 nm)/polymer

Example 4: Impact of Interference Stack where Multiple Layers ofTiO₂/SiO₂ are Used and their Impact on the Transmission and ReflectionProperties of a Substrate with Electrochromic Tungsten Oxide

The interference stack in this case between the glass and thetransparent conductor comprised of TiO₂ (45 nm)/SiO₂ (35 nm) in one caseand in the other case the stack was TiO₂ (40 nm)/SiO₂(10 nm)/TiO₂ (10nm)/SiO₂ (40 nm). As seen from the results in Table 8, the relativechange in transmission color (i.e., the % change between the two ΔE_(T)*values) from bleached to the colored state was rather modest, but wassignificant in terms of reducing the reflection color change, where thelatter stack was superior.

TABLE 8 Comparison of optical properties of different interferencestacks with SiO2 and TiO2 Normal Angle Transmission TransmissionReflectance Reflectance Bleached Colored Bleached Colored L* a* b* L* a*b* L* a* b* L* a* b* Sample (T) (T) (T) (T) (T) (T) ΔE_(T)* (R) (R) (R)(R) (R) (R) ΔE_(R)* Glass/TiO2(45 nm)/ 92.7 0.8 9.2 54.4 1.8 −5.5 41.045.7 −3.5 −20.9 41.1 −11.2 −18.9 9.2 SiO2(35 nm)/ ITO(120 nm)/WO3 (400nm)/polymer Glass/TiO2(40 nm)/ 92.0 5.3 8.9 53.2 0.9 −6.8 42.1 47.9−17.0 −19.1 44.7 −19.9 −13.9 6.7 SiO2(10 nm)/TiO2 (10 nm) SiO2(40nm)/ITO (120 nm)/WO3 (400 nm)/polymer

Table 9 shows the impact of transmission and reflection at variouswavelengths for the two stacks. This shows that the average reflectivityis in a similar range, but the reflected color is different.

TABLE 9 Comparison of the two stacks with different configuration withSiO2/TiO2 on EC properties Glass/TiO2(45 nm)/SiO2(35 nm)/ Glass/TiO2(40nm)/SiO2(10 nm)/TiO2(10 nm) ITO(120 nm)/WO3(400 nm)/polymer SiO2(40nm)/ITO(120 nm)/WO3(400 nm)/polymer Wavelength Bleached Colored BleachedColored (nm) % T % R % T % R % T % R % T % R 400 52.9 40.4 22.8 22.855.3 37.7 23.3 20.9 450 63.8 33.1 26.5 20.1 64.3 32.7 25.9 22.0 500 85.211.6 23.3 18.5 83.0 13.9 22.8 20.1 550 77.7 19.8 22.1 12.8 73.4 24.220.7 18.2 600 90.4 6.7 22.2 6.3 87.4 9.8 21.3 10.0 650 83.4 14.3 21.75.8 85.5 12.0 21.3 7.2 700 80.2 16.1 21.1 6.2 78.7 17.7 20.9 7.0

Table 10 compares the properties of using the stack TiO₂ (40 nm)/SiO₂(10 nm)/TiO₂ (10 nm)/SiO₂(40 nm) at normal angle and at 30 degrees. Theresults show that the difference in ΔE_(R)* between the two cases islarger as compared to when the stack was a two-layer stack TiO₂ (45nm)/SiO₂ (35 nm) (see Table 5). The relative difference at the twoangles is 31% ((8.8−6.7)/6.7). This compares to 12% in Table 5. Thisresult shows that although use of increasing the number of layers (e.g.,two vs four layers) and optimizing them can reduce the reflectivitychanges from bleached to colored at small angles, but such windows willshow a larger color difference at off/angle.

TABLE 10 Normal and off-angle comparison when using stack TiO2(40nm)/SiO2(10 nm)/TiO2(10 nm)/SiO2(40 nm) Normal Angle Off angle (30°)Reflectance Reflectance Reflectance Reflectance Bleached ColoredBleached Colored L* a* b* L* a* b* L* a* b* L* a* b* (T) (T) (T) (T) (T)(T) ΔE_(R)* (R) (R) (R) (R) (R) (R) ΔE_(R)* 47.9 −17.0 −19.1 44.7 −19.9−13.9 6.7 33.4 1.8 −19.5 33.2 −6.6 −16.9 8.8

Example 5: Impact of Interference Stack on the Transmission Color andReflected Color of a Substrate in Contact with a Thick ElectrochromicMedium

As compared to the above two examples, the configuration of the EChalf-cell with the interference stack resembles the one shown in FIG. 6which is substrate 21 b, interference stack 26 b, TC 23 b and the thickEC medium 27 b which is also an electrolyte. When no interference stackis present, the half-cell is like a prior-art cell shown in FIG. 2b witha substrate 11 a, TC 13 a and in contact with a thick electrolyticmedium 17 a (thickness greater than 10 μm). The results show thatalthough in both cells the color change in transmission is small, a verylarge reduction is seen in the color change in reflection ΔE_(R)* (from18.9 to 5.1) as the cell optical state is changed from bleached tocolored. The dye absorption constant was selected to give the sameamount of coloration as tungsten oxide in Example 2.

TABLE 11 Impact on transmission and reflection changes by using a stackfor an EC system with a thick EC medium Normal Angle TransmissionTransmission Reflectance Reflectance Bleached Colored Bleached ColoredL* a* b* L* a* b* L* a* b* L* a* b* Sample (T) (T) (T) (T) (T) (T)ΔE_(T) (R) (R) (R) (R) (R) (R) ΔE_(R)* Glass/ITO(120 nm)/ 99.7 −6.4 10.834.3 1.4 −13.9 67.5 28.1 0.6 7.9 10.8 8.0 9.6 18.9 Dye(300 um)Glass/TiO2(40 nm)/ 90.5 −1.7 11.9 31.6 3.1 −12.7 64.1 51.9 −11.1 −0.947.1 −12.6 −2.0 5.1 SiO2(10 nm)/ITO (120 nm)/Dye (300 um)/

Example 6: Fabrication and Testing of Half Cells

The following half-cell samples were made as shown in Table 12. Thesubstrate in all cases was standard soda-lime glass. The first substraterefers to one of the substrates used to fabricate the EC cells whichwill be on the front of the window, i.e., placed in the window such thatit is on the outside with the side with the reflective layer facinginwards. All of the substrates with or without reflective coatings wereobtained from Nippon Sheet Glass (NSG) (Toledo, Ohio). Stack 1 and Stack2 refer to two types of reflective stacks provided by NSG. In Stack 2,one of the coatings in the reflective stack also provided a gold/browntint, coatings in stack 1 were clear coatings containing TiO₂/SiO₂.Please note that in the sample names “NRC” stands for no reflective(interference) coating, “RC1” stands for reflective coating Type 1, and“RC2” for reflective coating Type 2.

TABLE 12 Details for the first substrate used to fabricate EC devicesSubstrate TC Tungsten Substrate Reflective thickness, resistivity OxideSample tint stack mm TC* Ω/▭ thickness, nm Clear-NRC^(#) Clear No 2.3TEC ™15 15 400 Blue-RC1 Tinted Stack1 6 ITO 10 360 Gray-RC1 TintedStack1 6 ITO 10 360 Brown-Gold-RC2 Bronze Tinted Stack2 6 ITO 12 360Gold-RC2 Clear Stack2 6 ITO 12 360 *TC = Transparent conductor,^(#)Clear non reflective glass is thinner glass as compared to othersITO = Indium/tin Oxide, TEC ™15 was obtained from NSG, Toledo, OH

These substrates were evaluated for reflectivity, transmission,transmitted color and the reflected color with the glass side (uncoatedside) facing the light source using Ultrascan® XE instrument (made byHunter Lab, Reston, Va.). For all measurements a D65 illuminant and2-degree observer was used. For reflectivity measurements, a black feltbackground was used to measure reflectivity. The felt was soaked inpropylene carbonate (RI=1.42). These measurements were made when thetungsten oxide was in the bleached state and then when tungsten oxidewas colored in a liquid electrolyte cells containing propylene carbonateand 0.025M lithium salt (lithium bis-(trifluoromethanesulfonyl)imide).For coloration, platinum counter electrode and a silver wire dipped in asolution of AgNO₃ in acetonitrile was used for a reference electrodeusing coloring potential of −0.9V and bleaching a potential of 0.2V wasused against the reference applied for 2 minutes for the partiallycolored state. The same setup was used applying −1.3 V for 3 minutes forthe fully colored state. The measurements of percentage transmission (%T) measured at normal incidence are shown in Table 13. In addition,color was measured both in transmission and reflection for these halfcells. The latter was measured from the non-coated side. Table 14 showsthe difference in color in going from bleached to partially colored andalso in going from bleach to the fully colored state.

TABLE 13 % Transmission values in bleached, partially colored and fullycolored state State of % T Wavelength, nm Sample Sample 400 450 500 550600 650 700 Clear-NRC Fully colored 22.71 17.14 7.9 2.93 1.02 0.38 0.15Partially colored 35.96 35.77 24.87 13.75 6.71 3.14 1.57 Bleached 50.6467.19 69.96 69.45 67.49 70 65.65 Gray-RC1 Fully colored 7.95 7.52 5.034.32 2.87 2.4 2.91 Partially colored 16.93 17.21 11.76 10.36 6.27 4.985.79 Bleached 27.48 31.54 25.5 35.05 28.86 23.9 34.97 Blue-RC1 Fullycolored 10.86 12.04 8.14 5.36 2.92 2.03 1.98 Partially colored 24.7531.99 23.4 18.94 9.8 6.91 6.74 Bleached 33.57 45.48 40.91 42.64 31.1421.44 24.74 Brown Gold-RC2 Fully colored 1.98 3.14 3.18 3.93 4.17 3.73.86 Partially colored 4.58 6.83 6.15 7.34 6.29 5.01 5.01 Bleached 7.7112.74 13.9 28.66 31.05 23.96 36.76 Gold-RC2 Fully colored 3.15 5.89 5.85.36 4.68 3.78 3.26 Partially colored 6.22 13.44 13.88 15.89 12.82 10.179.06 Bleached 9.81 20.25 29.87 42.97 56.41 36.72 44.85

TABLE 14 Comparison between ΔE_(T)* and ΔE_(R)* between bleached,partially colored and fully colored half cells ΔE* Reflection, ΔE_(R)*Transmission, ΔE_(T)* Bleached Bleached Bleached Bleached Half Cell vsPartially vs Fully vs Partially vs Fully Sample Colored Colored ColoredColored Clear- 8.93 8.96 57.31 80.63 NRC Gray-RC1 2.28 4.67 31.88 41.58Blue-RC1 1.64 3.19 24.44 43.75 Brown 1.75 5.74 38.24 41.86 Gold-RC2Gold-RC2 3.91 8.97 39.84 56.27

As expected and desired, large color differences are seen in colorvalues when measured in transmission. Gray-RC1, Blue-RC1 andBrown-Gold-RC2 samples showed a surprisingly small change in color inreflection. The blue colored glass also has a color spectrum that isclose to the color spectrum of colored tungsten oxide in the visibleregion. The Gold-RC2 sample showed significant color in deeply coloredstate, which shows that the shift in the reflective spectra can besensitive to the degree of coloration, particularly when it contrastswith the color of the colored EC coating.

Example 7

The tungsten oxide substrates used in Example 6 were used to assemble ECcells using a TEC™15 substrates of thickness 2.2 mm as counter electrodeas shown in FIGS. 2a with the exception that these cells did not have anEC2 layer, i.e. the counter electrode did not have the EC2 coating.Electrolyte was a 300 μm thick layer containing a redox dye species inpropylene carbonate, that is the electrolyte has electrochromicproperties. The electrolyte also comprised of lithiumbis(trifluoromethanesulfonyl)imide, polymethyl methacrylate to increaseviscosity and UV stabilizers. Different dye mixtures were used—Dye-B thecomposition which resulted in a blue appearance in transmission when thecell colored and Dye-N the composition which resulted in more neutralappearance. Table 15 below provides the details on the sampleconstruction; all samples have tungsten oxide coatings as shown in Table12. In Table 15, “S1” refers to this set of samples in this batch todistinguish these from a different batch of samples.

TABLE 15 EC cell (or panels) details made using front substrates inTable 12 First Counter First substrate electrode, or Dye type Substrate*Reflective type of second in Sample ID color stack substrate electrolyteS1-Clear-NRC-N Clear No TEC ™15 Dye-N S1-Clear-NRC-B Clear No TEC ™15Dye-B S1-Blue-RC1-N Blue Tinted Stack1 TEC ™15 Dye-N S1-Blue-RC1-B BlueTinted Stack1 TEC ™15 Dye-B S1-Bluegreen- Bluegreen Stack1 TEC ™15 Dye-NRC1-N Tinted S1-Bluegreen- Bluegreen Stack1 TEC ™15 Dye-B RC1-B TintedS1-Gray-RC1-N Gray Tinted Stack1 TEC ™15 Dye-N S1-Gray-RC1-B Gray TintedStack1 TEC ™15 Dye-B S1-Brown-Gold- Bronze Stack2 TEC ™15 Dye-N RC2-NTinted S1-Brown-Gold- Bronze Stack2 TEC ™15 Dye-B RC2-B TintedS1-Gold-RC2-N Clear Stack2 TEC ™15 Dye-N S1-Gold-RC2-B Clear Stack2TEC ™15 Dye-B *Substrate details are listed in Table 1.

The cells were measured in the bleached state and then colored using 1.3V applied for 3 minutes and measured in transmission to calculate colordifference between the bleached and the colored states as shown Table16. The color differences are large in a range of about 40 to 80 units.In addition, ΔE_(T-H)* numbers show the shift in the transmitted lighthue as the EC panel transitions from the fully bleached to the coloredstate. In many instances this change may not be important depending onthe degree of illumination provided by this window, and in some cases itis desirable that this be small so that the incoming light does notacquire a different hue and change the visual perception of the objects.ΔE_(T-HA)* less than 15 are desirable and in another embodiment numbersless than 10 and yet in another embodiment numbers less than about 5.This number or the transmitted light color can be substantially alteredeven if the same tungsten oxide is used, by changing the color of thedye.

TABLE 16 Color in Transmission of cells for colored and bleached stateand color difference Bleached Colored Sample L* a* b* L* a* b* ΔE_(T)*ΔE_(T-H)* S1-Clear-NRC-N 82.5 −3.2 5.0 23.8 −0.3 8.5 58.9 4.6S1-Clear-NRC-B 83.5 −3.8 11.0 30.7 7.2 −46.4 78.8 58.4 S1-Blue-RC1-N60.3 −0.6 3.5 16.5 3.3 6.7 44.1 5.1 S1-Blue-RC1-B 59.6 −2.2 6.8 19.4 8.6−35.8 59.6 44.0 S1-Bluegreen-RC1-N 65.1 −9.4 −4.7 15.8 1.4 4.1 51.2 14.0S1-Bluegreen-RC1-B 65.5 −10.1 −1.8 25.7 5.8 −41.2 58.2 42.5S1-Gray-RC1-N 56.9 1.0 27.9 15.4 5.0 17.6 43.0 11.0 S1-Gray-RC1-B 56.46.5 29.4 28.8 −3.4 −3.7 44.2 34.6 S1-Brown-Gold-RC2-N 70.7 2.8 32.4 21.14.4 20.3 51.1 12.2 S1-Brown-Gold-RC2-B 69.6 1.9 35.4 19.9 −2.4 −23.677.3 59.1The same cells were measured in reflection (Table 17), and the colorchanges in reflection (ΔE_(R)*) are substantially smaller for the cellswhich had the reflective coatings, all below 6 and some below 3. Thisshows that even though there are vast differences in the color change intransmission as seen in Table 16 (ΔE_(T)*), the change in reflectedcolor is small for cells with the interference stack (less than 6 whencolored). Substrates with no reflective layer (Samples S1-Clear-NRC-Nand S1-Clear-NRC-B) show a high value of ΔE_(R)*. For the clear glasswith “N” coloring dye, even though ΔE_(R-H)* is small (1.5), but ΔE_(R)*is high (11.1). Since the latter number is high, this would still beseen by a casual observer outside during the daytime as a very differentappearance. For most desirable characteristics both ΔE_(R-H)* andΔE_(R)* should be small. Limitations in reflectivity on ΔE_(R)* havebeen discussed earlier, and for ΔE_(R-H)* these should be less than 5 inone embodiment and less than 3 in another embodiment.

TABLE 17 Color in Reflection of EC cells for colored and bleached statesand color difference Bleached Colored Sample L* a* b* L* a* b* ΔE_(R)*ΔE_(R-H)* S1-Clear-NRC-N 39.5 −1.0 0.1 28.5 0.5 0.5 11.1 1.5S1-Clear-NRC-B 39.6 −1.0 3.4 28.5 1.2 −4.9 14.1 8.6 S1-Blue-RC1-N 31.1−2.4 −1.2 28.5 −2.5 −0.2 2.9 1.1 S1-Blue-RC1-B 31.2 −2.1 −1.2 28.6 −1.5−2.0 2.9 1.1 S1-Bluegreen-RC1-N 32.4 −6.8 −0.7 35.7 −7.3 −5.0 5.4 4.3S1-Bluegreen-RC1-B 31.5 −5.4 −4.2 35.1 −7.6 −4.9 4.4 2.4 S1-Gray-RC1-N39.7 3.4 14.6 38.5 −0.8 12.6 4.8 4.7 S1-Gray-RC1-B 40.5 3.1 11.7 39.41.4 10.6 2.3 2.0 S1-Brown-Gold-RC2-N 51.6 −4.7 23.8 53.2 −2.4 25.2 3.12.7 S1-Brown-Gold-RC2-B 51.8 −2.6 23.5 53.7 −4.8 24.9 3.3 2.7Table 18 condenses the data on color change from Tables 16 and 17, forreflection and transmission. First, this data shows that for a givencell, whether it is blue coloring (B) or neutral coloring (N) there is alarge color difference ΔE_(T)* between bleached and colored states(range 43-79). However, the reflection change ΔE_(R)* is large for clearcell ranging from 11 to 14 for the two dyes, whereas for all the cellswith reflective layer this number is smaller than 6 and for some smallerthan 3.In addition, this table also compares the colored state of cells withneutral coloring and the blue coloring dyes. The tungsten oxide used forthe blue coloring cell is the same as the neutral coloring cell for eachtype of substrate. It is interesting to note that in the colored statethere are large differences in transmitted color but the reflected colordifferences are much smaller (all less than 6). This also shows that thereflectivity is dominated in these cells by the front substrate. Thepresence of reflective coatings substantially lowers the colordifference in reflection. As an example, comparing cells S1-Blue-RC1-Nand S1-Blue-RC1-B,s both with a blue tinted substrate and theinterference coating but with different dye result in small differencesin reflected color but with a high difference in transmitted color. Thisshows that even though to an outside observer the colors of these twopanels in the colored state will appear to be similar, but a personinside the building would see a significant difference in the lightspectrum being transmitted.

TABLE 18 Comparison between ΔE_(T)* and ΔE_(R)* of colored and bleachedstates of cells using both dye compositions ΔE_(R)* (Reflection) ΔE_(T)*(Transmission) Bleached Dye-N vs Dye-N vs Bleached Dye-N vs Dye-N vs vsDye-B Dye-B vs Dye-B Dye-B Sample Colored Bleached Colored ColoredBleached Colored S1-Clear-NRC-N 11.1 3.4 5.5 58.9 6.1 55.8S1-Clear-NRC-B 14.1 78.8 S1-Blue-RC1-N 2.9 0.3 2.1 44.1 3.8 42.9S1-Blue-RC1-B 2.9 59.6 S1-Bluegreen-RC1-N 5.4 3.9 0.7 51.2 3 46.6S1-Bluegreen-RC1-B 4.4 58.2 S1-Gray-RC1-N 4.8 3.1 3.1 43 5.8 26.6S1-Gray-RC1-B 2.3 44.2 S1-Brown-Gold-RC2-N 3.1 2.2 2.5 51.1 3.4 44.3S1-Brown-Gold-RC2-B 3.3 77.3The transmission and reflection data as a function of wavelength areshown in Tables 19 and 20, to show both the extent of coloration andreflection. This table also shows % T ratios of the cells in bleached tocolor state at 550 nm, which is a measure of the extent of coloration.There are several values above 5 which provided low change in reflectedcolor as seen in Table 18. For the blue tinted substrates with both thedyes the contrast value (% T bleached/% T colored) at 550 nm exceeds 10.

TABLE 19 Transmission spectra for cells in the colored and bleachedstates Bleach to Color State of % T Wavelength, nm ratio at SampleSample 400 450 500 550 600 650 700 550 nm S1-Clear- Colored 5.5 2.650.65 6.95 3.93 1.63 0.88 9.1 NRC-N Bleached 22.33 57.53 59.41 62.9660.72 57.94 55.12 S1-Clear- Colored 0.55 29.14 17.34 4.47 1.52 3.42 5.714.4 NRC-B Bleached 34.73 51.58 59.12 64.42 64.01 62.78 61.57 S1-Gray-Colored 3.23 1.45 0.39 3.46 2.39 1.58 1.64 8.7 RC1-N Bleached 12.9725.14 27.2 30.03 28.66 24.85 30.76 S1-Gray- Colored 0.3 13 6.8 2.16 0.71.97 5.73 14.2 RC1-B Bleached 19.41 22.93 24 30.58 27.3 23.93 31.99S1-Blue- Colored 2.88 1.62 0.4 3.47 2.02 1.12 1.02 10.4 RC1-N Bleached13.85 36.01 41.51 36.26 29.4 21.42 21.39 S1-Blue- Colored 0.6 20.1612.06 3.47 1.05 2.05 4.3 10.9 RC1-B Bleached 24.27 33.95 39.8 37.65 29.821.78 22.93 S1- Colored 9.27 6.1 2.56 10.7 7.64 4.75 3.46 4.9 Bluegreen-Bleached 25.48 45.85 52.23 52.23 48.97 37.34 32.61 RC1-N S1- Colored5.17 29.33 24.61 14.14 7.8 8.17 8.92 3.6 Bluegreen- Bleached 30.56 41.8151.96 50.77 49.59 37.9 32.79 RC1-B S1-Brown- Colored 0.7 0.56 0.2 2.652.72 1.9 1.65 10.3 Gold-RC2- Bleached 3.31 11.64 14.37 27.32 28.48 26.2933.46 N S1-Brown- Colored 0.8 6.65 6.88 5.85 4.49 5.66 8.15 3.9Gold-RC2- Bleached 5.57 9.32 15.9 22.58 33.31 25.84 29.61 B S1-Gold-Colored 1.16 1.09 0.45 4.48 4.32 2.87 2.27 8.7 RC2-N Bleached 5.25 17.5431.6 39.01 54.22 41.14 40.76 S1-Gold- Colored 0.07 8.53 6.85 2.26 0.952.83 6.78 17.3 RC2-B Bleached 6.74 15.4 27.7 39.04 51.22 39.71 42.22

TABLE 20 Reflection spectra for cells in the colored and bleached statesState of % R Wavelength, nm Sample Sample 400 450 500 550 600 650 700S1-Clear- Colored 7.69 5.09 5.95 5.42 5.73 6.17 5.62 NRC-N Bleached 9.849.68 12.03 10.95 10.72 11.05 16.53 S1-Clear- Colored 7.5 6.39 6.43 5.345.43 5.95 5.46 NRC-B Bleached 12.41 8.53 11.28 11.05 11.07 11.62 18.9S1-Gray- Colored 5.65 5.39 5.93 5.94 5.14 5.14 5.53 RC1-N Bleached 7.37.61 6.41 7.62 5.55 6.88 10.44 S1-Gray- Colored 5.89 6 6.21 5.8 5.16 5.66.25 RC1-B Bleached 7.57 7.51 6.59 7.57 5.66 7.07 10.64 S1-Blue- Colored9.61 12.29 8.78 10.85 6.11 6.72 7.69 RC1-N Bleached 6.77 6.96 8.24 8.015.93 5.33 4.99 S1-Blue- Colored 9.22 11.7 9.22 10.14 5.95 6.69 7.53RC1-B Bleached 6.2 7.77 8.6 7.05 5.58 5.45 5.21 S1- Colored 8.7 8.510.94 9.93 7.85 7.01 6.29 Bluegreen- Bleached 12.64 15.52 12.39 15.018.48 11.16 11.68 RC1-N S1- Colored 7.25 9.5 11.25 8.96 6.93 7.42 6.64Bluegreen- Bleached 10.82 13.64 12.79 13.82 8.46 11.26 11.42 RC1-BS1-Brown- Colored 5.71 6.45 7.98 11.14 11.1 10.35 11.75 Gold-RC2-NBleached 5.46 6.51 8.61 11.29 12.39 15.78 16.8 S1-Brown- Colored 7.167.28 9.04 11.07 12.02 12.23 12.38 Gold-RC2-B Bleached 7.24 7.7 9.5711.85 12.64 16.17 16.95 S1-Gold- Colored 6.21 10.71 14.94 23.81 20.5231.68 31.35 RC2-N Bleached 6.5 8.85 15.37 20.96 21.44 19.22 19.02S1-Gold- Colored 6.89 11.29 14.18 25.56 19.4 30.7 32.16 RC2-B Bleached6.82 9.7 15.4 20.76 21.76 23.13 21.18

Example 8: Impact of Glass Tint and Interference Stack on LightReflectivity and Transmission for an EC Device

Another set of EC cells (or EC panels) were made (Set 2) similar to theones made in Example 7, in terms of the device construction and the typeof the tungsten oxide used. The electrolyte also used the two dyes asabove, one of which resulted in a blue coloring cell and the other oneresulted in more neutral coloring cell. The electrolyte comprised ofpropylene carbonate, lithium bis(trifluoromethanesulfonyl)imide, andcontained polymethyl methacrylate to increase viscosity and UVstabilizers. The substrates were selected as in Table 21, all of whichwere 6 mm in thickness for the front substrate and 2.2 mm for the rearsubstrate. The substrates with the tint and/or the interference coatingswere obtained from NSG, and then ITO was deposited on them as explainedin Example 7. Description of the substrates used, and other EC celldetails are in Table 21. In the sample detail “S2” refers to the secondset of the samples, the color refers to the overall color of thesubstrate, “B” stands for a blue coloring cell, “N” for a neutralcoloring cell, and “RC” stands for the cell having an interferencecoating, and “NRC” for a cell not having an interference coating. Thesamples where the Cell-ID is underlined this table had the sameconfiguration as those used in Example 7 (Table 15).

TABLE 21 EC cell details made using front color substrates with andwithout reflective coating First Counter Description First substrateelectrode, or Dye type (all tungsten Substrate* Reflective type ofsecond in Cell ID coated) color stack substrate electrolyteS2-Clear-NRC-N Clear non Clear None TEC ™15 Dye-N reflectiveS2-Clear-RC1-N Clear reflective Clear Stack1 TEC ™15 Dye-NS2-Clear-RC1-B Clear reflective Clear Stack1 TEC ™15 Dye-B S2-Gold-RC2-NGold reflective Clear Stack2 TEC ™15 Dye-N S2-Gold-RC2-B Gold reflectiveClear Stack2 TEC ™15 Dye-B S2-Blue-NRC-N Blue non reflective Blue NoneTEC ™15 Dye-N tinted S2-Blue-RC1-N Blue reflective Blue Stack1 TEC ™15Dye-N tinted S2-Bronze-NRC-N Bronze non Bronze None TEC ™15 Dye-Nreflective tinted S2-Bronze-NRC-B Bronze non Bronze None TEC ™15 Dye-Breflective tinted S2-Gray-RC1-N Gray reflective Gray Stack1 TEC ™15Dye-N tinted S2-Gray-RC1-B Gray reflective Gray Stack1 TEC ™15 Dye-Btinted

The above cells were used to measure color and spectra in transmissionand in reflection at normal angle. All of these cells exhibited largechange in transmitted color as desired and expected.

TABLE 22 Color measurement in transmission (Normal angle) of EC cellsBleached Colored Sample ID L* a* b* L* a* b* ΔE_(T)* S2-Clear-NRC-N 90.3−2.2 4.4 34.2 6.5 5.0 56.7 S2-Clear-RC1-N 87.3 −3.1 4.3 28.8 7.0 4.159.3 S2-Clear-RC1-B 85.9 −4.3 9.7 44.1 −12.2 −35.9 62.3 S2-Gold-RC2-N73.5 3.4 31.4 21.2 5.8 16.7 54.3 S2-Gold-RC2-B 73.6 2.5 35.6 34.1 −16.9−13.8 66.2 S2-Blue-NRC-N 72.9 −10.7 −6.6 21.0 3.0 −0.4 54.0S2-Blue-RC1-N 71.7 −12.5 −5.7 19.6 3.5 0.5 54.9 S2-Bronze-NRC-N 73.3 1.98.0 25.3 6.0 6.0 48.3 S2-Bronze-NRC-B 72.8 2.8 12.4 35.9 −8.7 −28.9 56.5S2-Gray-RC1-N 64.4 −0.6 2.0 18.5 5.1 2.7 46.3 S2-Gray-RC1-B 63.8 −2.45.7 29.9 −6.3 −30.8 49.9

The change in ΔE_(R)* in Table 23, shows that by depositing a clearinterference stack on clear glass (samples S2-Clear-NRC-N compared toS2-Clear-RC1-N) reduces the color change in reflection, which is notdifferent from the trend modeled for the half cells in Table 3. Thisshows that the presence of reflective stack decreases the change inreflection by a significant amount. This may also be seen in the pairS2-Blue-NRC-N and S2-Blue-RC1-N, both with the same dye and glass tintbut without and with reflective stack, where the change in reflectiondecreases from 8.2 to 4.2.

TABLE 23 Color measurement in reflection (Normal Angle) of EC cells,glass side of the substrate with interference layers facing frontReflectance Reflectance Bleached Colored Sample ID L* a* b* L* a* b*ΔE_(R)* S2-Clear-NRC-N 41.9 −4.9 −3.7 28.7 4.6 −5.4 16.3 S2-Clear-RC1-N46.7 −2.9 2.8 41.6 −7.1 7.6 8.1 S2-Clear-RC1-B 47.5 1.1 1.5 42.5 −0.50.8 5.4 S2-Gold-RC2-N 55.3 5.5 29.8 53.4 −2.3 27.8 8.2 S2-Gold-RC2-B53.9 7.2 27.3 53.7 4.8 29.1 3.0 S2-Blue-NRC-N 33.3 −4.5 −6.9 27.6 1.3−6.0 8.2 S2-Blue-RC1-N 34.6 −3.0 −4.4 31.3 −5.3 −3.1 4.2 S2-Bronze-NRC-N32.5 0.2 −1.2 27.2 1.7 −2.9 5.7 S2-Bronze-NRC-B 31.7 −1.1 0.9 26.0 0.2−5.6 8.8 S2-Gray-RC1-N 31.8 −0.9 0.0 29.3 −1.8 1.1 2.8 S2-Gray-RC1-B31.3 1.5 0.9 29.3 −0.5 −0.1 3.0

Table 23 also shows other trends. Tinting of the substrate also reducesthe reflectivity differences between the bleached and the coloredstates. This may be seen by comparing S2-Clear-NRC-N, S2-Blue-NRC-N,S2-Bronze-NRC-N and S2-Bronze-NRC-B, all of which have no reflectivestack and the last three substrates are tinted. The ΔE_(R)* for theseare respectively 16.3 (not tinted), 8.2, 5.7 and 8.8. ComparingS2-Bronze-NRC-N and S2-Bronze-NRC-B, the ΔE_(R)* for these are 8.8 and5.7 respectively, showing that when the EC coloration and the front tintsubstrate are similar there is a higher reduction in reflectivitydifferences. This is because the neutral coloring cell has a slightlyred/brown color which is closer to the Bronze in its color spectrum ofthe substrate.

Comparing Clear-N-NRC, Blue-N-NRC and Bronze-N-NRC where the ΔE_(R)* are16.3, 8.2 and 5.5 respectively for the same color dye but no-tint anddifferent tints, shows the importance of both the substrate tint, andits combination with the coloration of the EC cell.

Given all of these conclusions, both the presence of the interferencestack and the use of substrate tint are important to reduce ΔE_(R)*. Inaddition, these may be judiciously combined with the coloration of theEC cell to reduce the reflective differences even further.

Example 9: Impact of Glass Tint and Interference Stack on LightReflectivity and Transmission for an EC Device in an IGU Unit

EC cells listed in Table 21, were modelled for their thermal performancein an IGU unit. For this modelling “Window” program was used that ismade available by Lawrence Berkeley National Laboratory (Berkeley,Calif.). The results are shown in Table 24. The IGU construction placesthe EC panel (or EC cell) on the outside, and the inner glass pane waseither TEC10 Optiwhite™ (3 mm thick) or Suncool 70:40 ProT™ (6 mm thick)both from NSG. The inner panes are coated with a Low-e coating. TheseIGUs are assembled with a 12 mm gap between the EC panel and the Low-ecoated panel. The Low-e side faced the gap (surface 3), as shown for anIGU assembly in FIGS. 3, 5 and 6. The gap was filled with Argon. Solarheat gain coefficients (SHGC) and the thermal conductivity (U) for theseassemblies are shown in this table. The samples where the Cell-ID isunderlined in this table had the same configuration as those used inExample 7 (Table 15)

TABLE 24 Modelled IGU configuration, SHCG and U value IGU configurationU value Low-E SHGC SHGC Wm- ID Cell Gap Glass Bleached Colored 2K-1TEC-Ar-S2-Clear- S2-Clear-NRC- 12 mm TEC10 0.51 0.11 0.48 NRC-N N ArOptiwhite, TEC-Ar-S2-Clear- S2-Clear-RC1- gap 3 mm 0.45 0.10 0.48 RC1-NN TEC-Ar-S2-Clear- S2-Clear-RC1- 0.45 0.15 0.48 RC1-B B TEC-Ar-S2-Gold-

0.35 0.09 0.48 RC2-N

TEC-Ar-S2-Gold-

0.36 0.11 0.48 RC2-B

TEC-Ar-S2-Blue- S2-Blue-NRC- 0.27 0.10 0.48 NRC-N N TEC-Ar-S2-Blue-

0.26 0.10 0.48 RC1-N

TEC-Ar-S2-Bronze- S2-Bronze-NRC- 0.34 0.10 0.48 NRC-N NTEC-Ar-S2-Bronze- S2-Bronze-NRC- 0.36 0.13 0.48 NRC-B B TEC-Ar-S2-Gray-

0.27 0.10 0.48 RC1-N

TEC-Ar-S2-Gray-

0.27 0.12 0.48 RC1-B

SC-Ar-S2-Clear- S2-Clear-NRC- Suncool 0.39 0.09 0.40 NRC-N N 70:40SC-Ar-S2-Clear- S2-Clear-RC1- ProT, 0.36 0.08 0.40 RC1-N N 6 mmSC-Ar-S2-Clear- S2-Clear-RC1- 0.35 0.12 0.40 RC1-B B SC-Ar-S2-Gold-

0.26 0.07 0.40 RC2-N

SC-Ar-S2-Gold-

0.26 0.09 0.40 RC2-B

SC-Ar-S2-Blue- S2-Blue-NRC- 0.23 0.08 0.40 NRC-N N SC-Ar-S2-Blue-

0.22 0.08 0.40 RC1-N

SC-Ar-S2-Bronze- S2-Bronze-NRC- 0.26 0.08 0.40 NRC-N N SC-Ar-S2-Bronze-S2-Bronze-NRC- 0.27 0.11 0.40 NRC-B B SC-Ar-S2-Gray-

0.21 0.08 0.40 RC1-N

SC-Ar-S2-Gray-

0.21 0.10 0.40 RC1-B

Tables 25 and 26 show the color in transmission and in reflection forthe modelled IGUs and also the change in color in transmission ΔE_(T)*and in reflection ΔE_(R)* respectively. As expected and desired, thechange in transmission color is high when the EC panel changes from theclear state (bleached state) to the darker state (colored state). Table26 shows that the change in reflectivity for the clear glass with nointerference stack is the highest at 24.9.

TABLE 25 Optical properties (light transmission) of IGU with EC panelsBleached Colored IGU ID L* a* b* L* a* b* ΔE_(T) TEC-Ar-S2-Clear-NRC-84.6 −1.7 5.2 32.0 6.1 5.4 53.2 N TEC-Ar-S2-Clear-RC1- 82.0 −2.5 5.227.0 6.6 4.5 55.7 N TEC-Ar-S2-Clear-RC1- 80.8 −3.6 10.4 38.7 −11.6 −33.461.3 B TEC-Ar-S2-Gold-RC2- 69.8 4.0 30.9 20.0 5.6 16.2 51.9 NTEC-Ar-S2-Gold-RC2- 70.1 3.2 35.0 30.4 −15.8 −12.7 64.9 BTEC-Ar-S2-Blue-NRC- 67.7 −9.9 −5.4 19.2 2.8 0.1 50.4 NTEC-Ar-S2-Blue-RC1- 66.7 −11.5 −4.5 17.9 3.3 0.9 51.3 NTEC-Ar-S2-Bronze- 68.9 2.2 8.4 23.7 5.7 6.2 45.4 NRC-N TEC-Ar-S2-Bronze-68.5 3.1 12.7 31.3 −8.3 −26.8 55.3 NRC-B TEC-Ar-S2-Gray-RC1- 60.2 −0.32.7 17.0 4.8 3.1 43.6 N TEC-Ar-S2-Gray-RC1- 59.8 −1.9 6.3 25.6 −6.1−28.7 49.1 B SC-Ar-S2-Clear-NRC- 83.3 −5.4 3.5 31.6 5.1 4.5 52.8 NSC-Ar-S2-Clear-RC1-N 80.6 −6.2 3.5 26.4 5.7 3.7 55.5SC-Ar-S2-Clear-RC1-B 79.5 −7.2 8.6 38.4 −12.9 −33.6 59.2SC-Ar-S2-Gold-RC2-N 68.3 0.2 28.7 19.2 4.7 15.4 51.1 SC-Ar-S2-Gold-RC2-B68.6 −0.3 32.7 29.9 −17.2 −13.1 62.3 SC-Ar-S2-Blue-NRC-N 66.8 −12.5 −6.518.8 2.2 −0.4 50.6 SC-Ar-S2-Blue-RC1-N 65.8 −14.1 −5.6 17.5 2.7 0.4 51.5SC-Ar-S2-Bronze 67.8 −1.0 6.9 23.0 4.8 5.5 45.2 NRC-N SC-Ar-S2-Bronze-67.4 −0.2 11.1 31.1 −9.5 −27.0 53.4 NRC-B SC-Ar-S2-Gray-RC1-N 59.3 −3.11.5 16.5 4.1 2.5 43.4 SC-Ar-S2-Gray-RC1-B 58.8 −4.7 4.9 25.6 −7.0 −28.847.4

TABLE 26 Optical properties (light reflection) of IGU with EC panelsBleached Colored IGU ID L* a* b* L* a* b* ΔE_(R) TEC-Ar-S2-Clear- 50.7−6.1 0.5 28.9 4.6 −5.2 24.9 NRC-N TEC-Ar-S2-Clear- 53.5 −4.7 5.1 42.0−7.0 7.7 12.0 RC1-N TEC-Ar-S2-Clear- 53.7 −1.3 5.1 42.8 −0.8 −1.3 12.7RC1-B TEC-Ar-S2-Gold- 58.6 5.8 32.2 54.2 −2.3 27.8 10.1 RC2-NTEC-Ar-S2-Gold- 57.3 7.2 30.3 54.6 4.6 28.7 4.1 RC2-B TEC-Ar-S2-Blue-37.7 −7.4 −6.5 27.6 1.3 −5.9 13.4 NRC-N TEC-Ar-S2-Blue- 38.4 −6.2 −4.131.3 −5.3 −3.1 7.2 RC1-N TEC-Ar-S2-Bronze- 37.3 −0.1 1.9 27.3 1.7 −2.811.2 NRC-N TEC-Ar-S2-Bronze- 36.7 −0.7 4.6 26.2 0.0 −6.8 15.5 NRC-BTEC-Ar-S2-Gray- 34.6 −1.4 1.0 29.4 −1.8 1.1 5.2 RC1-N TEC-Ar-S2-Gray-34.0 0.5 2.3 29.4 −0.5 −0.9 5.7 RC1-B SC-Ar-S2-Clear- 45.6 −4.9 −3.128.6 4.6 −5.3 19.6 NRC-N SC-Ar-S2-Clear- 49.6 −3.3 2.8 42.0 −7.1 7.6 9.8RC1-N SC-Ar-S2-Clear- 50.1 0.4 2.3 42.6 −0.5 −0.4 8.0 RC1-BSC-Ar-S2-Gold- 57.1 5.6 30.6 54.2 −2.3 27.8 8.8 RC2-N SC-Ar-S2-Gold-55.7 7.3 28.4 54.6 4.7 28.9 2.8 RC2-B SC-Ar-S2-Blue- 35.0 −5.4 −7.5 27.61.3 −6.0 10.2 NRC-N SC-Ar-S2-Blue- 36.0 −4.1 −4.9 31.3 −5.3 −3.1 5.1RC1-N SC-Ar-S2-Bronze- 34.4 0.3 −0.5 27.3 1.7 −2.9 7.6 NRC-NSC-Ar-S2-Bronze- 34.0 −0.7 1.9 26.2 0.3 −6.3 11.3 NRC-B SC-Ar-S2-Gray-32.9 −0.9 0.0 29.4 −1.8 1.1 3.8 RC1-N SC-Ar-S2-Gray- 32.5 1.2 1.1 29.4−0.4 −0.5 3.8 RC1-B

Table 27 Shows a comparison of color changes in transmission andreflection changes for the EC panel, and the IGUs made by two differentlow-e coated glass. This table also includes change in hue both intransmission and reflection. A low hue change in transmission ΔE_(T-H)*(from bleached to the colored state) will allow the quality of light tobe unchanged as the EC device darkens. As seen in the tables, low huechange is obtained for those EC panels which darken to a neutral color.Furthermore, the substrate with a permanent gray tint and with theinterference layer also keeps both of ΔE_(R)* and ΔE_(R-H)*, low, whichprovides least visible change in reflection. This is seen for Lowreflective changes (ΔE_(R)* and ΔE_(R-H)*) and low transmissive huechanges (ΔE_(T-H)*) are also seen in both of the IGUs (e.g., see sampleS2-Gray-RC1-N. For a sample where a blue coloring EC device is selectedwith everything else remaining the same (sample S2-Gray-RC1-B),excepting for a large hue change in transmission, these cells alsoperform well in keeping the reflective changes low. Low change inreflectivity and low change in hue are also seen for sampleS2-Gold-RC2-B. This sample has no substrate tint, but the tint comes infrom one of the layers in the interference coating. For a given ECpanel, the choice of the low-e glass is important in the IGU, as thiscan exacerbate the reflectivity differences or even reduce them. As anExample, for sample S2-Clear-RC1-B, the ΔE_(R)* is acceptable at 5.4,but this changes to 12.7 when TEC is used as a low-e panel showing thisto be unacceptable, whereas with SC low-e glass, this IGU still has anacceptable value. In addition, the reflective hue also changed in thesame fashion. This effect was opposite for S2-Bronze-NRC-N, where TEChad more favorable reflective properties as compared to SC in the IGU.As discussed earlier in Table 24, all of these choices even if the ECcell is the same will also influence SHGC and important parameter in theselection process.

TABLE 27 Comparison of color changes in EC cell and the IGUs in whichthe EC cell is incorporated into Cell only IGU 1 (TEC-Ar) IGU 2 (SC-Ar)Cell ID ΔE_(T)* ΔE_(T-H)* ΔE_(R)* ΔE_(R-H)* ΔE_(T)* ΔE_(T-H)* ΔE_(R)*ΔE_(R-H)* ΔE_(T)* ΔE_(T-H)* ΔE_(R)* ΔE_(R-H)* S2-Clear-NRC-N 56.7 8.616.3 9.6 53.2 7.8 24.9 12.0 52.8 10.5 19.6 9.8 S2-Clear-RC1-N 59.3 10.18.1 6.4 55.7 9.1 12.0 3.4 55.5 11.9 9.8 6.1 S2-Clear-RC1-B 62.3 46.3 5.41.8 61.3 44.5 12.7 6.4 59.2 42.6 8.0 2.8 S2-Gold-RC2-N 54.3 14.8 8.2 8.051.9 14.8 10.1 9.2 51.1 14.0 8.8 8.4 S2-Gold-RC2-B 66.2 53.1 3.0 3.064.9 51.3 4.1 3.1 62.3 48.8 2.8 2.6 S2-Blue-NRC-N 54.0 15.0 8.2 6.0 50.413.8 13.4 8.7 50.6 15.9 10.2 6.9 S2-Blue-RC1-N 54.9 17.1 4.2 2.6 51.315.7 7.2 1.4 51.5 17.8 5.1 2.1 S2-Bronze-NRC-N 48.3 4.5 5.7 2.3 45.4 4.111.2 5.0 45.2 5.9 7.6 2.7 S2-Bronze-NRC-B 56.5 42.8 8.8 6.7 55.3 41.015.5 11.3 53.4 39.2 11.3 8.2 S2-Gray-RC1-N 46.3 5.7 2.8 1.4 43.6 5.1 5.20.4 43.4 7.3 3.8 1.4 S2-Gray-RC1-B 49.9 36.7 3.0 2.2 49.1 35.2 5.7 3.347.4 33.8 3.8 2.3

Example 10: Impact of Glass Tint and Interference Stack on LightReflectivity and Transmission for an EC Device with an ElectrolyteHaving Electrochromic Properties

EC cells were constructed using 6 mm thick front substrates, where someof these were tinted, and some of these had reflective layers as shownin Table 28. All of these were coated with ITO with a surfaceresistivity of about 12Ω/□. The counter electrode was 2.3 mm thickTEC™15 glass from NSG. These were assembled with a gap of 300 μm whichwas filled with an electrolyte composition comprising propylenecarbonate along with a blue coloring dye (Dye-B) with anodic andcathodic elements bridged together which was 4,4′-Bipyridinium,1-(4-ferrocenylbutyl)-1′-methyl cation withbis(trifluoromethanesulfonyl)imide anion. The electrolyte also containedpolymethyl methacrylate to increase viscosity and UV stabilizers. Thecolor of the colored EC cells in this dye is mainly dominated by thecathodic bipyridinium, and the anodic ferrocene component has only alittle contribution the colored region. The cells in Table 28 and otherswhich start with S3 do not have any EC coating, and all of theelectrochromic properties are derived from the EC dye in the electrolytebetween the two conductive coatings on the two substrates.

TABLE 28 EC cell details made using front color substrates with andwithout reflective coating and no EC coatings First Counter Firstsubstrate electrode, or Dye type Substrate* Reflective type of second inCell ID Description* color stack substrate electrolyte S3-Clear-NRC-BClear, non-reflective Clear None TEC ™15 Dye-B S3-Clear-RC1-B Clear,reflective Clear Stack1 TEC ™15 Dye-B clear S3-Gold-RC2-B Clearreflective Clear Stack2 TEC ™15 Dye-B (gold) S3-Blue-RC1-B Blue,non-reflective Blue None TEC ™15 Dye-B tinted S3-Blue-NRC-B Blue,reflective Blue Stack1 TEC ™15 Dye-B clear tinted *Descriptionsummarizes concisely the color of the first substrate and the reflectivecoating if present and its color which is also given in the next twocolumns

Table 29 lists the color properties of the cells in transmission atnormal angle, all of which show large changes in color and hue in goingfrom bleach to the colored state.

TABLE 29 Color measurement in transmission (Normal angle) of EC cellsBleached Colored Sample ID L* a* b* L* a* b* ΔE_(T)* ΔE_(T-H)* S3-Clear-89.8 −3.6 12.1 33.6 0.6 −51.7 85.2 63.9 NRC-B S3-Clear- 84.4 −0.8 7.532.2 2.2 −51.1 78.6 58.7 RC1-B S3-Gold- 69.8 6.5 31.2 20.5 −6.3 −30.379.8 62.8 RC2-B S3-Blue- 72.6 −11.8 2.8 26.4 1.1 −46.9 69.0 51.3 NRC-BS3-Blue- 69.1 −8.9 −1.5 26.6 2.4 −47.1 63.3 46.9 RC1-B

Table 30 lists the color properties of the cells in reflection at normalangle, all of which show large changes in color and hue in going frombleach to the colored state when the interference stack is not present.The results show that the substrate without tint and the reflectivelayer (S3-Clear-NRC-B) has a high change in color and hue in reflection.Sample S3-Blue-NRC-B does not have a reflective coating but thesubstrate is tinted. The other samples with the reflective layer havemuch lower reflective color and hue and is in the desired range. Eventhough, the sample S3-Clear-RC1-B has a ΔE_(R)* of 6.7, in the fullycolored state, but it must be recognized that there is a large reductionas compared to the sample without the interference stack where theΔE_(R)* is 14.0. Further we used a commercial glass with an interferencestack and in these samples the thickness of the transparent conductorwas not optimized. Therefore, this data should be viewed with theperspective of the incredible and surprising potential when interferencestacks are used.

TABLE 30 Color measurement in reflection (Normal Angle) of EC cells,glass side of the substrate with interference layers facing frontReflectance Reflectance Bleached Colored Sample ID L* a* b* L* a* b*ΔE_(R)* ΔE_(R-H)* S3-Clear- 41.9 2.1 −2.1 28.7 7.1 −15.2 19.2 14.0 NRC-BS3-Clear- 52.7 −5.6 14.2 46.5 −6.0 11.7 6.7 2.5 RC1-B S3-Gold- 59.5 2.031.9 57.7 0.8 29.8 3.0 2.5 RC2-B S3-Blue- 33.4 −1.9 −10.4 28.1 2.3 −14.68.0 6.1 NRC-B S3-Blue- 38.5 −9.1 −0.4 35.4 −7.8 −1.8 3.7 2.0 RC1-B

Table 31 summarizes all color differences in transmission and reflectionas well as the hue differences taken from Tables 29 and 30 for the dyeonly cells.

TABLE 31 Transmission vs Reflection color changes on dye only EC cellsSample ID ΔE_(T)* ΔE_(T−H)* ΔE_(R)* ΔE_(R−H)* S3-Clear-NRC-B 85.2 63.919.2 14.0 S3-Clear-RC1-B 78.6 58.7 6.7 2.5 S3-Gold-RC2-B 79.8 62.8 3.02.5 S3-Blue-NRC-B 69.0 51.3 8.0 6.1 S3-Blue-RC1-B 63.3 46.9 3.7 2.0

Table 32 lists the transmission properties of the cells at variouswavelengths. This shows that the bleach/color ratio (transmission ratio)of all of the cells is high exceeding 25. For cells S3-Gold-RC2-Bhighest contrast ratios are observed, which also shows least colorchange in reflectivity in Tables 30 and 31.

TABLE 32 Transmission spectra for EC cells Bleach/ State of % TWavelength, nm Color ratio Cell ID Sample 400 450 500 550 600 650 700 at55 nm S3-Clear-NRC- Bleached 51.1 60.7 72.6 78.5 77.3 75.3 72.6 29.4 BColored 0.6 37.7 20.6 2.7 0.7 4.9 23.4 S3-Clear-RC1- Bleached 47.2 56.163.5 65.0 67.0 68.4 66.6 26.3 B Colored 0.6 35.3 18.7 2.5 0.7 4.8 22.2S3-Gold-RC2- Bleached 9.7 19.1 30.6 39.7 51.3 54.9 56.2 33.4 B Colored0.2 11.6 8.3 1.2 0.4 3.2 17.3 S3-Blue-NRC- Bleached 34.8 41.2 48.2 49.536.5 30.7 33.4 31.9 B Colored 0.4 25.2 13.3 1.6 0.3 1.9 10.5S3-Blue-RC1- Bleached 33.6 40.1 43.2 42.8 32.8 28.3 30.7 25.2 B Colored0.5 25.4 13.0 1.7 0.4 2.1 10.4

Table 33 lists the reflection properties of the cells at variouswavelengths. This shows that the bleach/color ratio of all of the cellsis lower at 550 nm for cells with reflective coatings for substrateswith similar tints.

TABLE 33 Reflection spectra for cells Bleach/ State of % R Wavelength,nm Color ratio Cell ID Sample 400 450 500 550 600 650 700 at 550 nmS3-Clear- Bleached 17.4 13.0 12.1 12.4 12.9 12.2 11.3 2.4 NRC-B Colored13.8 10.1 6.1 5.2 5.6 5.9 6.3 S3-Clear- Bleached 15.4 13.5 18.3 23.020.8 17.4 16.0 1.3 RC1-B Colored 12.4 10.8 13.9 17.5 15.3 12.2 11.4S3-Gold- Bleached 9.0 10.9 19.1 29.6 34.2 28.8 24.0 1.1 RC2-B Colored9.0 10.6 18.0 27.9 31.1 25.4 20.8 S3-Blue- Bleached 10.5 11.2 9.1 7.96.2 5.7 5.8 1.6 NRC-B Colored 9.4 9.8 6.6 5.1 4.7 4.7 4.8 S3-Blue-Bleached 9.0 10.5 11.9 11.6 8.0 6.6 6.6 1.2 RC1-B Colored 7.9 9.4 10.09.6 6.7 5.8 5.8

Example 11: Dye Only Cells with Adhesively Bonded Films

Various films were bonded to the EC glass panels. Some of these filmshave a low-e surface, and while some others have UV blocking properties.A film with low emissivity surface was added to the second side of thedye only EC panel (that is the side which would face inside thebuilding. In another instance UV blocking film is generally added to thefirst side of the EC panel that faces outside of the building forproviding enhanced UV protection of the panel. Both the films may alsobe added on each of the respective surfaces.

This film SolarGard Ecolux™ 70 has a low emissivity surface and SX80 hasUV blocking properties, both from Saint Gobain. The latter film isparticularly designed for outdoor use, which is for bonding to the firstsurface. The dye only samples (without an EC coating) were prepared withthese bonded films as shown in Table 34.

TABLE 34 Dye only EC cell details made using front color substrates withand without reflective coating with additional films on outside surfacesof panel Film on First Film on Panel First substrate panel Descriptionsurface Substrate* Reflective surface Sample ID (Dye only) 1 color stack2 S3-Clear- Clear non None Clear None SolarGard NRC-Eco-B reflectiveEcolux ™ 70 S3-Clear- Clear None Clear Stack1 SolarGard RC1-Eco-Breflective Ecolux ™ 70 S3-Blue- Blue None Blue Stack1 SolarGardRC1-Eco-B reflective tinted Ecolux ™ 70 S3-Clear- Clear non SX80 ClearNone None NRC-SX80-B reflective S3-Clear- Clear SX80 Clear Stack1 NoneRC1-SX80-B reflective S3-Blue- Blue SX80 Blue Stack1 None RC1-SX80-Breflective tinted All of these EC samples use Dye-B in the electrolyteand use TEC15 counter electrode as second substrate

With films in place, color measurements were taken of the samples inbleached and fully colored state. As expected, the color values intransmission show a large change between the two states with the addedfilms (Table 35).

TABLE 35 Color measurement in transmission (Normal angle) of dye only ECcells with films on outside panel surfaces Bleached Colored Sample ID L*a* b* L* a* b* ΔE_(T)* ΔE_(T-H)* S3-Clear-NRC- 81.1 −2.1 20.4 27.7 −2.6−42.4 82.4 62.8 Eco-B S3-Clear-RC1- 76.5 0.2 16.0 27.2 −1.6 −41.9 76.057.9 Eco-B S3-Blue-RC1- 62.2 −8.1 6.0 22.1 −1.2 −39.0 60.7 45.6 Eco-BS3-Clear-NRC- 85.5 −6.8 9.8 43.4 −12.2 −41.7 66.7 51.8 SX80-BS3-Clear-RC1- 80.2 −4.1 5.3 36.6 −5.2 −45.9 67.2 51.2 SX80-BS3-Blue-RC1- 65.6 −10.8 −2.3 26.9 −0.4 −44.6 58.2 43.6 SX80-B

The color measurements of the cells in reflection (Table 36) show thatthe ΔE_(R)* values remain low for those cells with a reflective coatingand even lower for cells with both the reflective coating and a tint inthe glass. The additional SX80 film which is added to the first side ofthe EC cell or the addition of Ecolux™ film that is added on the secondside of the EC cell, both results in substantial reduction inreflectivity change when the EC cell transitions from clear to a darkeroptical state. The optical properties and the placement of these filmshas also an impact on the perceived color change which is lower for SX80as compared to Ecolux™. The higher reflectivity from the Ecolux™ filmand since it is placed after the light enters the EC cell, causes theΔE_(R)* to be higher.

TABLE 36 Color measurement in Reflection (Normal angle) of dye only ECcells with films on outside panel surfaces Bleached Colored Sample ID L*a* b* L* a* b* ΔE_(T)* ΔE_(T-H)* S3-Clear-NRC- 44.3 −2.9 −4.0 29.2 7.4−16.9 22.4 16.5 Eco-B S3-Clear-RC1- 53.5 −8.2 11.7 47.8 −7.3 7.0 7.5 4.8Eco-B S3-Blue-RC1- 39.0 −10.6 −1.0 35.0 −7.8 −1.6 4.9 2.8 Eco-BS3-Clear-NRC- 38.9 −0.3 −2.9 28.4 5.0 −13.0 15.5 11.4 SX80-BS3-Clear-RC1- 47.8 −8.1 12.1 42.6 −7.8 9.8 5.7 2.3 SX80-B S3-Blue-RC1-36.1 −9.1 −1.4 33.5 −7.6 −2.4 3.2 1.8 SX80-B

The color change data from the above two tables are summarized below inTable 37.

TABLE 37 Transmission vs Reflection color changes for dye only EC cellswith films on panel outside surfaces Sample ID ΔE_(T)* ΔE_(T−H)* ΔE_(R)*ΔE_(R−H)* S3-Clear-NRC-Eco-B 82.4 62.8 22.4 16.5 S3-Clear-RC1-Eco-B 35.229.3 7.5 4.8 S3-Blue-RC1-Eco-B 60.7 45.6 4.9 2.8 S3-Clear-NRC-SX80-B66.7 51.8 15.5 11.4 S3-Clear-RC1-SX80-B 67.2 51.2 5.7 2.3S3-Blue-RC1-SX80-B 58.2 43.6 3.2 1.8

Example 13: Transmissive and Reflective Color Changes in an EC Panelwith Depth of

coloration.

Two EC cells from the above table, S3-Clear-NRC-B and S3-Clear-RC1-B(see Table 28 for detailed description) were colored from the bleachedstate to completely colored state and then bleached. The first sampledoes not have a reflective stack, and the second sample does, both useclear substrates and a blue coring dye in the electrolyte. As shown fromthe traces in the figure the coloring voltage to the samples was appliedat about 30 seconds for the samples to start coloring from the bleachedstate. The samples reached the fully colored state at about 180 s. Ableach potential was applied at about 240 seconds and the samplereturned to the bleached state in about 400 seconds from the start. FIG.9 shows the data for these two samples as they are colored and bleached.This shows ΔE_(T)* vs time and compares to the change in transmissionchange at 550 nm with time. The change appears to be proportional toΔE_(T)* during this change in transmission. The L*, a* and b* valueswere measured continuously with time using Ultrascan® Pro instrumentfrom Hunterlab (Reston, Va.) both in reflection and in transmission.

FIG. 10 shows the change in ΔE_(T)* and ΔE_(R)* with time as the abovesamples color and bleach. This shows that although ΔE_(T)* continues tochange until the sample saturates (as was also seen in FIG. 9), theΔE_(R)* saturates out and reaches a plateau approximately when ΔE_(T)*reaches about 40. Therefore, this magnitude of ΔE_(T)* is used in theclaims, since the change in ΔE_(R)* is small beyond this value ofΔE_(T)*.

FIG. 11 shows change in ΔE_(R)* vs. ΔE_(T)* and Transmission Ratio (at550 nm) vs. ΔE_(T)* as the samples are colored. This also shows in adifferent graphical representation where ΔE_(R)* also initiallyincreases with an increase in ΔE_(T)*, until ΔE_(T)* reaches about 40,then there is a sharp inflexion and ΔE_(R)* stops changing. Thisinflexion is particularly sharp for the sample with the interferencestack. ΔE_(R)* also initially changes with the change in TransmissionRatio (at 550 nm) and then stops changing much beyond a transmissionratio of about 2.5. Thus, this magnitude of transmission ratio is usedin the claims for correlating to ΔE_(R)* changes. In embodiments whereno interference stack is used, the change in ΔE_(R)* shown by trianglesincreases beyond 10 and continues to increase even when the transmissionratio at 550 nm reaches a modest number of about 2. This means thatusing this disclosure, when this transmission ratio is greater than 2.5,e.g., even if it is 5 or 7 or 10 or greater, will still result inΔE_(R)* of less than 10 when reflection is viewed from the first side ofthe first substrate for the device containing the interference stack.This means that it is possible to lower the reflectivity changes for aVLTP panel substantially even though the transmission continues tochange.

When these EC panels are integrated in IGUs, the same is observed. Thisis because in an IGU the only part that changes its optical propertiesis the EC panel (or the VLTP), all of the other components are static.This means that in an IGU with a VLTP panel when the transmission ratio(bleached to the colored state) at 550 nm changes by the above amounts(i.e., a ratio of 2.5, or 5, or 7 or 10 or greater), the ΔE_(R)* changeis less than 10 and in many cases less than 10 when the reflection isobserved from the outside of the building or when looking during the dayfrom Surface 1 of the IGU. Surface 1 is shown for IGUs for example inFIGS. 3, 5 and 6. These IGUs may also have panels (substrates) withlow-e coatings or some of these may be tempered or even laminated,whether these form the VLTP panel or form other static panels in theIGU. Since all of these are static components, this means that this doesnot change the reflective characteristics as defined above when thetransmission of the IGU changes at 550 nm. The use of 550 nm as awavelength to measure the transmission changes is important as it is thepeak of the eye's photopic response, but other methods of visibletransmission measurement may also be used.

Concentrations, amounts, and other numerical data may be expressed orpresented herein in a range format. It is to be understood that such arange format is used merely for convenience and brevity and thus shouldbe interpreted flexibly to include not only the numerical valuesexplicitly recited as the limits of the range, but also to include allthe individual numerical values or sub-ranges encompassed within thatrange as if each numerical value and sub-range is explicitly recited. Asan illustration, a numerical range of “about 0.01 to 2.0” should beinterpreted to include not only the explicitly recited values of about0.01 to about 2.0, but also include individual values and sub-rangeswithin the indicated range. Thus, included in this numerical range areindividual values such as 0.5, 0.7, and 1.5, and sub-ranges such as from0.5 to 1.7, 0.7 to 1.5, and from 1.0 to 1.5, etc. Furthermore, such aninterpretation should apply regardless of the breadth of the range orthe characteristics being described. Additionally, it is noted that allpercentages are in weight, unless specified otherwise.

As used herein, the term “about” is used to provide flexibility to anumerical range endpoint by providing that a given value may be “alittle above” or “a little below” the endpoint. The degree offlexibility of this term can be dictated by the particular variable andwould be within the knowledge of those skilled in the art to determinebased on experience and the associated description herein. For example,in one aspect, the degree of flexibility can be within about ±10% of thenumerical value. In another aspect, the degree of flexibility can bewithin about ±5% of the numerical value. In a further aspect, the degreeof flexibility can be within about ±2%, ±1%, or ±0.05%, of the numericalvalue. Numerical quantities given are approximate, meaning that the term“around,” “about” or “approximately” can be inferred if not expresslystated.

The discussion, description, examples and embodiments presented withinthis disclosure are provided for clarity and understanding. A variety ofmaterials and configurations are presented, but there are a variety ofmethods, configurations and materials that may be used to produce thesame results. While the subject matter of this disclosure has beendescribed and shown in considerable detail with reference to certainillustrative embodiments, including various combinations andsub-combinations of features, those skilled in the art will readilyappreciate other embodiments and variations and modifications thereof asencompassed within the scope of the present disclosure. Moreover, thedescriptions of such embodiments, combinations, and sub-combinations isnot intended to convey that the claimed subject matter requires featuresor combinations of features other than those expressly recited in theclaims. Accordingly, the scope of this disclosure is intended to includeall modifications and variations encompassed within the spirit and scopeof the following appended claims.

We claim:
 1. An electrochromic variable light transmission panel (VLTP)comprising (a) a first transmissive substrate and a second transmissivesubstrate arranged in a parallel configuration; (b) wherein the firsttransmissive substrate comprises a first side and a second side, whereinthe second side is coated with a coating of a transparent conductor; (c)wherein the second transmissive substrate comprises a first side and asecond side, wherein the first side of the second substrate is coatedwith a transparent conductor; (d) wherein the first and secondtransmissive substrates are configured in an assembly such that anelectrochromic medium is disposed between the second side of the firsttransmissive substrate and the first side of the second transmissivesubstrate; wherein the VLTP is configured to have at least two opticalstates, wherein a bleached optical state is characterized by havinghigher light transmission, and a colored optical state is characterizedby having lower light transmission through the VLTP; and wherein theVLTP shows a transmission ratio of greater than 2.5 at 550 nm whenmeasured in the bleached state (optical state 1) and the colored state(optical state 2), and, in these optical states, shows ΔE_(R)* of lessthan 6 when reflection is viewed from the first side of the firsttransmissive substrate; wherein ΔE_(R)* is the color differenceaccording to CIELAB in reflection, wherein the color differences arecalculated as the Sqrt{(L₂*−L₁*)²+(a₂*−a₁*)²+(b₂*−b₁*)²}, wherein L₁*,a₁*, b₁*, L₂*, a₂*, and b₂* are values as defined by CIELAB to representlightness and color of the reflected light in the two optical states. 2.The electrochromic VLTP of claim 1, wherein the second side of the firsttransmissive substrate is coated with a stack of coatings comprising atleast two layers, followed by a coating of a transparent conductor. 3.The electrochromic VLTP of claim 1, wherein the first transmissivesubstrate is formed by laminating two clear substrates on oppositesurfaces of a transparent polymer film to form a laminate, wherein thelaminate has a first side and a second side which are not in contactwith the transparent polymer film, wherein the second side is coatedwith a coating of a transparent conductor.
 4. The electrochromic VLTP ofclaim 3, wherein the transparent polymer film is colored.
 5. Theelectrochromic VLTP of claim 3, wherein at least one side of one of thetwo clear substrates facing the transparent polymer film has a stack ofreflective coatings.
 6. The electrochromic VLTP of claim 1, wherein thefirst transmissive substrate is formed by laminating two clearsubstrates using two transparent polymer films to form a laminate,further comprising a third substrate having a stack of reflectivecoatings between the two transparent polymer films, and the laminate hasa first side and a second side which are not in contact with the twotransparent polymer films, wherein the second side of the laminate iscoated with a coating of a transparent conductor.
 7. The electrochromicVLTP of claim 6, wherein the third substrate is a flexible polymericfilm.
 8. An insulated glass unit (IGU) containing the electrochromicVLTP of claim
 1. 9. An insulated glass unit (IGU) containing theelectrochromic VLTP panel of claim
 6. 10. An electrochromic variablelight transmission panel (VLTP) comprising (a) a first transmissivesubstrate and a second transmissive substrate arranged in a parallelconfiguration; (b) wherein the first transmissive substrate comprises afirst side and a second side, wherein the second side of the firsttransmissive substrate is coated with a coating of a transparentconductor; (c) wherein the second transmissive substrate comprises afirst side and a second side, wherein the first side of the secondtransmissive substrate is coated with a transparent conductor; (d)wherein the first and second transmissive substrates are configured inan assembly such that an electrochromic medium is disposed between thesecond side of the first transmissive substrate and the first side ofthe second transmissive substrate; wherein the VLTP is configured tohave at least two optical states, wherein a bleached optical state ischaracterized by having higher light transmission, and a colored opticalstate is characterized by having lower light transmission through theVLTP; wherein the VLTP shows a transmission ratio of greater than 10 at550 nm when measured in the bleached (optical state 1) and the coloredstate (optical state 2), and, in these optical states, shows ΔE_(R)* ofless than 10 when reflection is viewed from the first side of the firstsubstrate; wherein ΔE_(R)* is the color difference according to CIELABin reflection, wherein the color differences are calculated as theSqrt{(L₂*−L₁*)²+(a₂*−a₁*)²+(b₂*−b₁*)²}, wherein L₁*, a₁*, b₁*, L₂*, a₂*,and b₂* are values as defined by CIELAB to represent lightness and colorof the reflected light in the two optical states.
 11. The electrochromicVLTP of claim 10, wherein the second side of the first transmissivesubstrate is coated with a stack of coatings comprising at least twolayers, followed by a coating of a transparent conductor.
 12. Theelectrochromic VLTP of claim 10, wherein the first transmissivesubstrate is formed by laminating two clear substrates on oppositesurfaces of a transparent polymer film to form a laminate, wherein thelaminate has a first side and a second side which are not in contactwith the transparent polymer film, wherein the second side of thelaminate is coated with a coating of a transparent conductor.
 13. Theelectrochromic VLTP of claim 12, wherein the transparent polymer film iscolored.
 14. The electrochromic VLTP of claim 12, wherein at least oneside of one of the two clear substrates facing the transparent polymerfilm has a stack of reflective coatings.
 15. An insulated glass unit(IGU) formed using the electrochromic VLTP of claim 10 and a thirdtransmissive substrate assembled in a parallel relationship to theelectrochromic VLTP, wherein the third transmissive substrate and theelectrochromic VLTP are separated by an edge spacer.
 16. The IGU ofclaim 15, wherein the third transmissive substrate surface has a Low-ecoating.
 17. The IGU of claim 15, wherein the third transmissivesubstrate is made of tempered glass.
 18. An insulated glass unit (IGU)comprising an assembly of at least one transmissive substrate assembledin parallel with a variable light transmission panel (VLTP) comprisingan electrochromic medium, wherein said assembly comprises a spacebetween said at least one transmissive substrate and said VLTP, whereinthe VLTP is configured to provide at least two optical states comprisinga bleached optical state and a colored optical state, wherein the VLTPis configured in the IGU to have a first surface facing outwardly,wherein the bleached optical state of the IGU is characterized by havinghigher light transmission than in the colored optical state; and the IGUshows a transmission ratio of greater than 10 at 550 nm when measured inthe bleached and the colored states, and, in these optical states, theIGU shows ΔE_(R)* of less than 10 when reflection is viewed from theside of the first surface; wherein ΔE_(R)* is the color differenceaccording to CIELAB in reflection, wherein the color differences arecalculated as the Sqrt{(L₂*−L₁*)²+(a₂*−a₁*)²+(b₂*−b₁*)²}, wherein L₁*,a₁*, b₁*, L₂*, a₂*, and b₂* are values as defined by CIELAB to representlightness and color of the reflected light in the two optical states.19. The IGU of claim 18, wherein the VLTP comprises: (a) a firsttransmissive substrate and a second transmissive substrate arranged in aparallel configuration; (b) wherein the first transmissive substratecomprises a first side and a second side, wherein the second side iscoated with a coating of a transparent conductor; (c) wherein the secondtransmissive substrate comprises a first side and a second side, whereinthe first side of the second substrate is coated with a transparentconductor; (d) wherein the first and second transmissive substrates areconfigured in an assembly such that an electrochromic medium is disposedbetween the second side of the first transmissive substrate and thefirst side of the second transmissive substrate.
 20. The IGU of claim19, wherein the second side of the first transmissive substrate iscoated with a stack of coatings comprising at least two layers, followedby a coating of a transparent conductor.
 21. The IGU of claim 19,wherein the first transmissive substrate is a laminated structure. 22.The IGU of claim 18, wherein the transmissive substrate has alow-emissivity (low-e) coating on one of its surfaces.
 23. The IGU ofclaim 18, wherein the transmissive substrate is tempered glass.